Category Archives: Quantum Physics

One of my all-time favorite plays is Copenhagen by Michael Frayn. The 1998 Tony Award winner tries to untangle the mysteries of a night in 1941 when German physicist Werner Heisenberg visited his mentor Niels Bohr at his home in the Danish capital. Bohr and Heisenberg had worked together to deduce the rules of quantum physics (known as the "Copenhagen model"), but now Heisenberg had a new boss, Adolf Hitler, who wanted an atomic bomb.

After a dinner prepared by Bohr's wife, Margarethe, Bohr and Heisenberg went for a walk in the garden. But instead of wandering for hours, as they often did while working on difficult problems, they quickly returned to the house. Heisenberg thanked Margarethe and showed himself out.

Soon after, the Bohrs fled Nazi-occupied Denmark in the middle of the night. They made their way to America, where Niels Bohr worked on the Manhattan Project. Meanwhile, Heisenberg became the head of the Nazi bomb project, which never even came close to producing a working weapon. Neither man ever revealed what they talked about that night. Did Heisenberg try to recruit Bohr for the Nazi bomb project? Was he there to ask his old mentor to check his math? Or did he carry a warning to Bohr? The three people present went to their graves keeping the secret. Frayn's play explores the possibilities, with the ghosts of the three people present reliving all the different interpretations of the events.

Kemp Powers' 2013 play, One Night in Miami, tries something similar. On February 25, 1964, Cassius Clay beat Sonny Liston to claim the heavyweight boxing title. In the crowd that night were Malcolm X, Sam Cooke, and Jim Brown. After the fight, instead of hitting the legendary Miami party circuit, the soon-to-be Muhammad Ali retreated to Malcolm X's hotel room, where they were later joined by Cooke and Brown. It was an unprecedented gathering of Black talent, and the weightiness of the evening was not apparent at the time. No one knows what they really talked about, but Powers' script imagines an evening that is equal parts celebratory and foreboding.

Actress Regina King chose to adapt One Night in Miami for her directorial debut after winning the Academy Award for Best Supporting Actress for 2018's If Beale Street Could Talk. King's first task was casting four of the most recognizable people in 20th-century history. It's hard to say who had the hardest job. Kingsley Ben-Adir, who recently played Barack Obama in The Comey Rule, portrays Malcolm X which means he's in the shadow of Denzel Washington's astounding performance in Spike Lee's biopic. Ballers' Eli Goree is Ali, a role that even the likes of Will Smith couldn't pull off convincingly. Aldis Hodge, MC Ren from Straight Outta Compton, plays Jim Brown, a man considered by some to be the greatest player in NFL history and who went on to a 50-year career in film and television. As Sam Cooke, Leslie Odom Jr. at least has the advantage of a great singing voice, since he originated the role of Aaron Burr in Hamilton on Broadway.

Crafting these performances to perfection is clearly where King's head is at and rightly so. All four of her leads turn out to be stellar. Goree's Ali is, improbably, the best of the bunch. He can both deliver the legendary bombast and reveal a thoughtful vulnerability in private. Ben-Adir's Malcolm X is on the receiving end of most of that vulnerability. In Powers' script, Malcolm X is the most morally ambivalent character, who intends to use the publicity surrounding his friend's historic championship to launch his schism with the Nation of Islam. But it is Malcolm who convinces Sam Cooke to stop devoting his talent to sappy love songs and push socially conscious works like "A Change is Gonna Come."

One Night in Miami lacks Copenhagen's experimental streak, but it functions beautifully as a four-handed character sketch of some of the most important Black men of the 20th century. (It's undoubtedly more entertaining when I saw Copenhagen performed live, half the audience left during intermission.) King's cameras pace restlessly around the room, finding framing that keeps all four actors in view, as they would appear onstage. This is a film that carefully doles out close-ups, and more directors should heed King's example. The film loses momentum when the group breaks up, and each character gets a little exposition designed to educate the audience on their historical importance. But when the four legends are together in the same room, One Night in Miami crackles with the fire of life.

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The Greatest: Four Legends Gather in One Night in Miami - Memphis Flyer

LONDON, Jan. 13, 2021 /PRNewswire/ --Raytheon UK, a unit of Raytheon Technologies (NYSE: RTX), alongside strategic partner Capita, received a contract award to provide the Royal Navy with transformative technology, training and learning solutions over the next 12 years.

The contract, which will be led by Capita, has an initial contract value of 200 million to Raytheon UK and will ensure the Royal Navy offers best-in-class training to all its service personnel. It will accelerate the use of new technology, processes and learning solutions, aligning with the Royal Navy's transformation agenda and positioning it to thrive in the 21st century.

"This announcement allows the team to begin efforts to transform the Royal Navy's training and learning solutions, and to modernise and transform the way training is delivered across the Armed Forces," said Jeff Lewis, chief executive of Raytheon UK. "Our extensive experience in leading large and complex transformative change programmes around the world will provide the Royal Navy with tailored, digitally enabled training, fit for the future."

Raytheon UK will play a key role in modernising and transforming the Royal Navy's training analysis, design, delivery, assurance, and management/support services, helping to make the UK Armed Forces more agile and adaptable than ever to tackle future challenges.

"We are committed to investing in the UK and helping to keep the country secure and our Armed Forces equipped with the best affordable sovereign solutions, creating highly skilled jobs across the UK," Lewis said. "We look forward to delivering these solutions to the Royal Navy over the coming years."

Rear Adm. Phil Hally MBE, the Royal Navy's director of people and training, said, "The award of this 12-year contract marks a major milestone for Navy transformation. It will see the modernisation of the RN training system at scale to deliver the operational capabilities of the future, unlock more opportunities for our people, and get better trained people to the frontline, quicker."

About Raytheon UKWith facilities in Broughton, Waddington, Glenrothes, Harlow, Gloucester and Manchester, Raytheon UK is invested in the British workforce and the development of UK technology. Across the country the company employs 1,700 people. As a prime contractor and major supplier to the U.K. Ministry of Defence, Raytheon UK continues to invest in research and development, supporting innovation and technological advances across the country.

Raytheon UK is a unit of Raytheon Technologies and sits within the Raytheon Intelligence & Space business.

About Raytheon TechnologiesRaytheon Technologies Corporation is an aerospace and defense company that provides advanced systems and services for commercial, military and government customers worldwide. With four industry-leading businesses Collins Aerospace Systems, Pratt & Whitney, Raytheon Intelligence & Space and Raytheon Missiles & Defense the company delivers solutions that push the boundaries in avionics, cybersecurity, directed energy, electric propulsion, hypersonics, and quantum physics. The company, formed in 2020 through the combination of Raytheon Company and the United Technologies Corporation aerospace businesses, is headquartered inWaltham, Massachusetts.

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Raytheon UK part of team transforming the Royal Navy's technology, training and learning solutions - PRNewswire

Abstract

Optical trapping and manipulation have been widely applied to biological systems, and their cutting-edge techniques are creating current trends in nanomaterial sciences. The resonant absorption of materials induces not only the energy transfer from photons to quantum mechanical motion of electrons but also the momentum transfer between them, resulting in dissipative optical forces that drive the macroscopic mechanical motion of the particles. However, optical manipulation, according to the quantum mechanical properties of individual nanoparticles, is still challenging. Here, we demonstrate selective transportation of nanodiamonds with and without nitrogen-vacancy centers by balancing resonant absorption and scattering forces induced by two different-colored lasers counterpropagating along a nanofiber. Furthermore, we propose a methodology for precisely determining the absorption cross sections for single nanoparticles by monitoring the optically driven motion, which is called as optical force spectroscopy. This method provides a novel direction in optical manipulation technology toward development of functional nanomaterials and quantum devices.

Nanoparticles and nanomaterialssuch as quantum dots, nanocrystals, carbon nanomaterials, molecular aggregates, and metal nanoparticleshave attracted great attention owing to their unique mechanical and quantum mechanical properties and have been used in various photonic, electronic, mechanical, and biomedical devices, such as light emitters, solar cells, photocatalysts, molecular electronics, structural materials, drug delivery, and bioimaging (16). Because these properties of nanoparticles/nanomaterials are strongly influenced by the surrounding environment and are significantly different from the bulk properties, such as quantum size effect, the characterization of individual nanoparticles provides important knowledge for advancing nanomaterial and quantum material sciences. Furthermore, the selection and sorting of single nanoparticles according to their characteristics are essential and desired for the precise design of functional nanostructures and development of single-quantum sensors, single-photon sources, and quantum information devices (7, 8).

Optical trapping and manipulation based on optical forces are promising tools for positioning, transporting, and aligning fine particles without mechanical contacts (9, 10). Optical tweezers proposed by Ashkin et al. have been used in various research fields, such as biophysics, cell biology, microfluidics, total analytical systems, and micromechanics (11, 12). Optical sorting of dielectric objects has been developed using holographic optics, flow cytometry, interference technology, and near field photonics (1315). Metal nanoparticles can also be separated by optical forces based on the surface plasmon resonances (16). However, these techniques are limited to the particle selection by the size and refractive index. The optical gradient and scattering forces exerted on small particles and their dependences on the diameter, wavelength, and relative refractive index are determined by the Mie theory. Furthermore, the reported methods are applicable only to the sorting of submicrometer or larger-sized dielectric particles. Trapping and manipulation of smaller-sized particles remain challenging because the optical force becomes weaker in proportion to the particle volume.

In this study, we demonstrate the optical selection and sorting of nanoparticles according to their quantum mechanical properties. Semiconductor quantum dots exhibit characteristic optoelectronic properties due to the quantum confinement of the electron-hole pairs in the nanovolume (1, 2). Diamond nanoparticles exhibit quantum resonances of point defects (17, 18). The optical forces reflect these quantum mechanical properties of nanoparticles and their optical characteristics (19, 20). The interaction between light and nanomaterials induces not only an energy transfer from the photons to the quantum mechanical motion of the electrons but also a momentum transfer between them. The change in the photon momentum give rise to optical forces, which drive the macroscopic mechanical motion of the nanoparticles. We note that there are three types of optical forces: (i) gradient force arising from the inhomogeneous intensity distribution of the electric field, (ii) dissipative scattering force caused by the real part of the refractive index, and (iii) quantum resonant absorption force exerted on nanomaterials. Therefore, we can realize the characterization and selective manipulation of single nanoparticles having various properties by monitoring and controlling the particle motions. This methodology provides a new direction in optical force technology toward advances in nanomaterial sciences.

To realize the sorting of individual nanoparticles, we use counterpropagating different-colored lasers that can extract the resonant absorption force by cancelling out the scattering forces. The counterpropagating beam systems were constructed using a pair of lenses with large numerical aperture placed opposite to each other (21) and the inversely directed evanescent waves (16). However, it is difficult to exclude the influence of the gradient force that easily negates the small effect of the quantum resonance force. Thus, we focused on tapered optical fibers, i.e., nanofibers (22, 23). We prepared a nanofiber with a diameter of several hundred nanometers and length of several millimeters (24), which exhibited the characteristics of single-mode propagation, thereby forming an intense evanescent field around the fiber and enabling long-distance propagation while maintaining a tightly focused beam of light. Using these characteristics, a uniform electric field distribution could be generated along the fiber by which the particle motion was restricted to one dimension. In addition, the optical gradient force and thermophoretic force, arising from the temperature gradient (e.g., Soret effect), were exerted in a direction perpendicular to the fiber axis such that the particle motion along the nanofiber was driven only by the resonant absorption and scattering forces. Furthermore, because the momentum of the photons in a waveguide depends on the propagation constants of the individual modes, the single-mode wave in our nanofiber had the constant photon momentum; this provides an ideal platform for analyzing the optical forces exerted on the nanoparticles. On the basis of the balance of the absorption and scattering forces induced by the different-colored lasers counterpropagating along the nanofiber, we succeeded in achieving the selective transportation of single nanoparticles according to the quantum resonant absorption (Fig. 1A).

(A) Concept of optical force absorption spectroscopy. By monitoring the mechanical motion of a single nanoparticle driven by optical forces, the resonant absorption properties can be analyzed with high sensitivity. Using two different-colored lasers counterpropagating along a nanofiber, a nanoparticle is trapped by the gradient force and transported by the absorption and scattering forces. The laser powers are adjusted to cancel out the scattering forces such that the particle moves depending on the absorption cross section. (B) Experimental setup. GR and NIR diode lasers are introduced from both ends of a nanofiber. The laser powers are measured by photodiodes (PD1 and PD2) and controlled by rotational neutral density filters to balance the forces. To record the motion of nanoparticles, a weak red laser is used, and its scattered light is monitored using a microscope-attached charge-coupled device (CCD) camera with filters to cut the strong scattered light of the GR and NIR lasers.

In addition to the selection and sorting, the proposed system can precisely determine the resonant absorption cross sections of single nanoparticles. Fluorescence and photothermal spectroscopies have been widely used for characterizing single nanoparticles and nanomaterials because of their high sensitivity at the level of single-molecule detection (25, 26). However, these methods probe the relaxation processes emitting a photon and thermal energy, which are regarded as indirect absorption measurements. When the excited states of the materials irreversibly transit to other states without undergoing relaxation processes, such as photochemical reactions, these techniques can no longer observe the resonant absorption. Absorption spectroscopy, which directly measures the excitation processes, is an indispensable tool for analyzing the interaction strengths between light and matter. In particular, the absolute values of the absorption cross sections of single nanoparticles/nanomaterials are essential for experimental physics in material science and are crucial for designing nanostructured materials at a single-quantum state level (27). However, it is still challenging to detect extremely small absorption signals of single nanoparticles and nanomaterials. In our method, accurate measurement of quantum resonant absorption is realized by precisely observing the optical forcedriven motions of the nanoparticles, called as optical force spectroscopy. This spectroscopy based on the optical momentum change instead of the energy change is conceptually different from the conventional techniques.

Figure 1B illustrates the experimental setup. A nanofiber with a diameter of 400 nm was fabricated from a commercial single-mode optical fiber (24). The diameter is constant in the waist part of the fiber over a length of several hundred micrometers. The nanofiber was soaked in an aqueous solution of diamond nanoparticles, i.e., nanodiamonds (NDs). Because nitrogen-vacancy centers (NVCs) in NDs have superior properties, such as no photobleaching, high sensitivity to the surrounding environment, and sharp zero phonon line absorption, they have been gaining attention as luminescent and magnetic-responsive nanomaterials that can be used for biological imaging, sensing, and single-photon source (17, 18). Thus, selection and sorting of NDs with and without NVCs are highly desirable. We prepared two types of NDs; one contained NVCs (>300 per particle), i.e., quantum resonant ND (r-ND), and the other was almost free from the NVCs, i.e., nonresonant ND (n-ND). The diameters of both r-NDs and n-NDs were 50 15 nm. Continuous-wave green (GR; 532 nm) and near-infrared (NIR; 1064 nm) diode lasers were launched from both ends of the nanofiber. The NVCs exhibit absorption at the GR region but not at the NIR region (28, 29). Furthermore, we introduce a weak red laser in the fiber as a probe light (690 nm, 0.1 mW) to monitor the motion of the NDs, which was recorded by an optical microscope equipped with a charge-coupled device (CCD) camera.

Figure 2A depicts the trapping and transportation of a single r-ND, where only the GR laser (70 mW) is incident from the left end of the fiber and the motion of the r-ND is observed in the waist part of the fiber. The result shows that the r-ND is attracted by the gradient force of the evanescent field and moves along the fiber because of the dissipative forces. The particle speed is constant at 110 m/s (see a trajectory in fig. S1). We evaluate the force exerted on the r-ND as 89 fN by considering the balance between the optical force and viscous drag using the Faxen formula for correcting the effect of the fiber surface [(23) and see the Supplementary Materials). When the NIR laser is simultaneously incident from the other end of the fiber (from the right), where the NIR laser power is fixed at 250 mW, and the GR laser power is varied from 70 to 0 mW, we achieve the motion control of a single r-ND (Fig. 2B). At the GR laser power of 70 mW, the r-ND moves toward the propagation direction of the GR laser (from left to right). As the GR laser power decreases, the motion decelerates and subsequently stops (~8 s). On further decreasing the GR laser power, the r-ND moves toward the opposite direction. The motion control experiment for an n-ND is illustrated in the Supplementary Materials (fig. S3).

(A) Time-sequential images of the r-ND observed at 2-s intervals. The GR laser is incident from the left end (70 mW). A single r-ND is trapped and transported along the nanofiber at the velocity of 110 m/s. (B) Time-sequential images of the r-ND observed at 4-s interval. The GR laser is incident from the left end of a nanofiber and the NIR laser from the opposite end. The power of the NIR laser is fixed at 250 mW, and the GR laser power is changed from 70 to 0 mW. At approximately 8 s, the optical forces exerted by the two lasers balance each other. The white bar indicates a scale of 100 m. The dotted line represents the nanofiber position.

The dissipative optical force exerted on an r-ND along a nanofiber is composed of two components, namely, absorption and scattering forces (Fabs, Fsca), which are represented by the absorption and scattering cross sections (abs, sca), as followsF=Fabs+Fsca=neffIc(abs+sca)(1)where I and c represent the intensity and velocity of light in a vacuum, respectively, and neff is the effective refractive index of the nanofiber (neff = 1.354 at 532 nm). The scattering cross section for Rayleigh particles is theoretically given bysca=1285n2V234(n12n22n122n22)2(2)where n1 and n2 are the refractive indices of diamond and surrounding water, respectively, is the incident laser wavelength in vacuum, and V is the volume of the particle. In the case of r-NDs including NVCs, abs is given by the transition dipole strength of an NVC and the number of NVCs in r-ND. The NIR laser induces only the scattering force, as NVCs exhibit no absorption at 1064 nm.

We perform a motion control experiment for an n-ND without NVCs to measure the balanced powers of the GR and NIR lasers for restricting the motion of the particle. The NIR laser power was fixed at 160 mW, corresponding to the intensity of 108 MW/cm2 estimated from the mode profile of the nanofiber, while the observed balanced power of the GR laser was 7.61 mW (intensity, 6.06 MW/cm2). As Fabs is not exerted on the n-ND, scattering forces (Fsca) by the GR and NIR lasers balance each other. Moreover, sca strongly depends on the wavelength (Eq. 2), which is compensated by the large difference between the intensities of the GR and NIR lasers. As sca is proportional to the square of the particle volume, the scattering force also changes significantly depending on the particle size. Fortunately, the ratio of the scattering forces at 532 and 1064 nm is constant for any particle size. This is because the volume dependence of sca is the same (V2) for both wavelengths. Thus, it is noted that the balanced powers of the two counterpropagating lasers remain unchanged for n-NDs of any size.

Furthermore, we demonstrate the selective transportation of r-NDs and n-NDs (Fig. 3 and movie S1). The same experimental setup and nanofiber were used, and the NIR laser power was 160 mW. The GR laser power was adjusted to 7.40 mW to drive different motions of the r-NDs and n-NDs. This value is slightly lower than the balanced power of the n-ND such that the scattering force exerted by the NIR laser is stronger for n-NDs than that by the GR laser, whereas the resonant absorption force on the r-NDs by the GR laser reverses the force strength relation. By switching the probe laser on and off, we can measure the emission from the NVCs and thus distinguish between the r-NDs and n-NDs. The two particles at both ends are r-NDs (numbered 1 and 4) and the other two particles are n-NDs (numbered 2 and 3). Scattered light spots of four NDs have nearly the same intensities when the probe laser is off, while the spots of r-NDs are brighter than the spots of n-NDs in Fig. 3 because the NVC emission is added to the scattered light. The r-NDs slowly move to the right (along the propagation direction of the GR laser), whereas the n-NDs move in the opposite direction (see trajectories in fig. S2). This result clearly demonstrates the selective transportation of NDs according to the quantum resonant absorption of NVCs by using the optical forces.

Time-sequential images observed at 2-s intervals. Numbers indicate individual NDs. Particles 1 and 4 represent r-NDs, and particles 2 and 3 represent n-NDs, which is confirmed by the emission of the NVCs. The powers of GR and NIR lasers are set at 7.40 and 160 mW, respectively. The r-NDs move to the right (direction of GR laser propagation), whereas the n-NDs move toward the opposite direction. The white bar indicates a scale of 100 m. The dashed line represents the nanofiber position.

Next, we analyze the absorption cross section (abs) of a single r-ND. We prepared the same experimental conditions and used the same nanofiber that was used for the balanced power measurement of an n-ND. At the NIR laser power of 160 mW, the balanced power of the GR lasers for an r-ND was measured to be 6.75 mW (intensity, 5.37 MW/cm2). Then, by turning the NIR laser off, the motion of r-NDs driven by the GR laser was observed to determine the strength of the optical force. On the basis of the balance with the viscous drag, the optical force composed of Fabs and Fsca was calculated as 6.30 fN. As a reference, the data of the n-ND were used for the present absorption analysis. By comparing the balanced powers of the GR laser for the r-ND (Pr-ND = 6.75 mW) and n-ND (Pn-ND = 7.61 mW), we obtain the ratio of Fabs and Fsca exerted on the r-ND as (Pn-ND Pr-ND):Pr-ND (Fig. 4) such that the measured optical force on the r-ND (F = 6.30 fN) can be decomposed into Fabs = 0.71 fN and Fsca = 5.59 fN. This result demonstrates that the absorption and scattering forces exerted on a single r-ND can be separately determined with subfemtonewton order accuracy. Thus, from Eq. 1, we evaluate the abs to be 2.9 1014 cm2. We repeated the measurements for 10 different r-NDs using the same nanofiber to perform the experiments under the same conditions. The average and SD of the evaluated abs were 3.3 1014 and 1.1 1014 cm2, respectively. The deviations in abs can be attributed to the variations in the number of NVCs contained in the r-NDs with different sizes and defect densities. The detailed distribution of abs and estimated number of NVCs are shown in the Supplementary Materials (see fig. S4).

The sum of the absorption and scattering forces exerted on the r-ND under GR laser irradiation (1 = 532 nm) with the power Pr-ND being balanced by the scattering force exerted by the NIR (2 = 1064 nm) laser. For the n-ND having no absorbers, the scattering forces exerted by the GR laser with Pn-ND and the NIR laser with constant power balance each other. From these balances, the ratio of the absorption and scattering forces on the ND can be determined as (Pn-ND Pr-ND):Pr-ND.

Here, we emphasize that the present method can detect the absorption cross section in the order of a square nanometer, which is close to those of single molecules (typically as large as 1015 cm2). Under the diffraction-limited illumination condition, this absorption cross section corresponds to a transmittance of ~106. Recently, Kukura et al. (30) and Celebrano et al. (31) succeeded in measuring the extremely small absorption using highly sensitive detectors, and the accuracy of their method is comparable with that of our method. However, in their technique, the Rayleigh scattering caused by nanoparticles and nanomaterials attenuates the transmitted light intensity as well such that the absorption signals cannot be extracted separately from the scattering components. In contrast, our proposed optical force spectroscopy can separately determine the absorption and scattering cross sections of single nanoparticles from the momentum change. The sensitivity is not limited by the signal-to-noise ratio of light intensity detection but restricted by the accuracy of the motion detection. Although nanometer-level position sensing techniques are available, the random thermal motion is the main factor that determines the accuracy. If the experiment is performed using superfluid helium at the cryogenic temperature, then the detection accuracy will be ultimately improved.

We demonstrated the selective transportation of single nanoparticles based on the relation between the quantum mechanical properties of nanomaterials and their macroscopic motion driven by the quantum resonant optical forces. This selective transportation is applicable to the precise sorting of nanocrystals, quantum dots, and molecular nanoparticles according to their resonant absorption properties. Optical force spectroscopy directly and sensitively measures the interaction between light and nanoparticles separately from the scattering effects based on the photon momentum change and not the energy change. It is noted that even if the reference nanoparticle having the same parent material but without absorbers is unavailable, the proposed absorption detection can still be achieved (see Materials and Methods). Although we focus on NDs as the samples for the first demonstration, note that other kinds of nanoparticles can be equally interesting targets. Size-selective optical transport of semiconductor quantum dots has been successfully demonstrated (32). Furthermore, it was reported that organic dye-doped nanoparticles have unique optical trapping characteristics according to their quantum resonance properties (33, 34). Applying the present technique to these nanomaterials will be our future endeavor. In conclusion, we believe that our scheme can enable a new class of optical force methodologies to investigate the characteristics of advanced nanomaterials and quantum materials and develop state-of-the-art nanodevices.

We used commercially available NDs having a mean diameter of 50 nm (r-NDs, FND Biotech Inc.; n-NDs, Microdiamant Japan. The absorption of NVCs appears at 532 nm after proton irradiation for fabricating r-NDs; contrarily, n-NDs exhibit no absorption at 532 nm. These were dispersed in pure water with 0.1 weight % surfactant. The concentration was adjusted such that a single ND is trapped by a nanofiber during the experiment.

A commercially available single-mode optical fiber (780HP, Thorlabs) was used to fabricate a nanofiber. It was heated with a ceramic heater at ~1400C and stretched at both ends. The waist diameter of the nanofiber used in this study was 400 nm, which remained constant (variation of <2%) over a length of several hundred micrometers. From the mode dispersion curve obtained by the fiber mode analysis, the single-mode propagation is valid when the wavelength of incident light is longer than 360 nm. The fiber was fixed on a glass slide using ultraviolet glue and soaked in a cell filled with an ND-dispersed aqueous solution.

Continuous-wave GR (532 nm) and NIR (1064 nm) diode lasers were introduced from both ends of the fabricated nanofiber. The laser powers were controlled using rotational neutral density filters. To record the motions of the NDs, we introduced a weak red laser (690 nm), and its light, scattered light from the particles, was monitored using a CCD camera. When nanoparticles other than the observed particles are trapped on the fiber, their scattering reduces the laser intensity irradiated on the particle. To avoid this disturbance, the experiments were performed after ensuring no change in the transmitted laser power.

When the reference nanoparticle having the same parent material but containing no absorbers is unavailable, the proposed absorption detection can still be realized by the following method: The measurement of the balanced laser powers for the reference particle is replaced by the calculation of the ratio of the scattering cross sections at two different wavelengths (using Eq. 2). When the refractive index of the parent material is constant at two laser wavelengths, the ratio of the scattering cross sections can be obtained using the inverse fourth power law. Using this value, we can determine the balanced laser powers for the virtual nonabsorbing particle. We analyzed the same data for 10 r-NDs as the abovementioned experiments but without using the data for n-NDs; consequently, the absorption cross sections were determined as (3.8 1.0) 1014 cm2. The variation from the above value [(3.3 1.1) 1014 cm2] would have been caused by a deviation from the Rayleigh scattering theory (Eq. 2) owing to the shape, size, and refractive index of the particles, as well as the random and systematic errors in the measurements.

Acknowledgments: Funding: The authors acknowledge the funding received from JSPS KAKENHI (grant numbers JP16H06504, JP16H06506, JP18H03882, JP18H05205, JP17K05016, and JP19H04529) and the Cooperative Research Program of Network Joint Research Center for Materials and Devices. Author contributions: H.I. and K.S. developed the concept and supervised the experiments. K.Y., H.F., and K.S. conducted the experiments. H.I. and T.W. theoretically elucidated the phenomena. H.F., K.Y., T.W., H.I., and K.S. participated in discussion of the results. H.F., H.I., and K.S. prepared the manuscript. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

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Optical selection and sorting of nanoparticles according to quantum mechanical properties - Science Advances

Seeing our world through the eyes of a migratory bird would be a rather spooky experience. Something about their visual system allows them to 'see' our planet's magnetic field, a clever trick of quantum physics, and biochemistry that helps them navigate vast distances.

Now, for the first time ever, scientists from the University of Tokyo have directly observed a key reaction hypothesised to be behind birds', and many other creatures', talents for sensing the direction of the planet's poles.

Importantly, this is evidence of quantum physics directly affecting a biochemical reaction in a cell something we've long hypothesised but haven't seen in action before.

Using a tailor-made microscope sensitive to faint flashes of light, the team watched a culture of human cells containing a special light-sensitive material respond dynamically to changes in a magnetic field.

A cell's fluorescence dimming as a magnetic field passes over it. (Ikeya and Woodward, CC BY 4.0)

The change the researchers observed in the lab match just what would be expected if a quirky quantum effect was responsible for the illuminating reaction.

"We've not modified or added anything to these cells,"saysbiophysicist Jonathan Woodward.

"We think we have extremely strong evidence that we've observed a purely quantum mechanical process affecting chemical activity at the cellular level."

So how are cells, particularly human cells, capable of responding to magnetic fields?

While there are several hypotheses out there, many researchers think the ability is due to a unique quantum reaction involving photoreceptors called cryptochromes.

Cyrptochromes are found in the cells of many species and are involved in regulating circadian rhythms. In species of migratory birds, dogs, and other species, they're linked to the mysterious ability to sense magnetic fields.

In fact, while most of us can't see magnetic fields, our own cells definitelycontain cryptochromes.And there's evidence that even though it's not conscious, humans are actually still capable of detecting Earth's magnetism.

To see the reaction within cyrptochromes in action, the researchers bathed a culture of human cells containing cryptochromes in blue light caused them to fluoresce weakly. As they glowed, the team swept magnetic fields of various frequencies repeatedly over the cells.

They found that each time the magnetic field passed over the cells, their fluorescent dipped around 3.5 percent enough to show a direct reaction.

So how can a magnetic field affect a photoreceptor?

It all comes down to something called spin an innate property of electrons.

We already know that spin is significantly affected by magnetic fields. Arrange electrons in the right way around an atom, and collect enough of them together in one place, and the resulting mass of material can be made to move using nothing more than a weak magnetic field like the one that surrounds our planet.

This is all well and good if you want to make a needle for a navigational compass. But with no obvious signs of magnetically-sensitive chunks of material inside pigeon skulls, physicists have had to think smaller.

In 1975, a Max Planck Institute researcher named Klaus Schulten developed a theory on how magnetic fields could influence chemical reactions.

It involved something called a radical pair.

A garden-variety radical is an electron in the outer shell of an atom that isn't partnered with a second electron.

Sometimes these bachelor electrons can adopt a wingman in another atom to form a radical pair. The two stay unpaired but thanks to a shared history are considered entangled, which in quantum terms means their spins will eerily correspond no matter how far apart they are.

Since this correlation can't be explained by ongoing physical connections, it's purely a quantum activity, something even Albert Einstein considered 'spooky'.

In the hustle-bustle of a living cell, their entanglement will be fleeting. But even these briefly correlating spins should last just long enough to make a subtle difference in the way their respective parent atoms behave.

In this experiment, as the magnetic field passed over the cells, the corresponding dip in fluorescence suggests that the generation of radical pairs had been affected.

An interesting consequence of the research could be in how even weak magnetic fields could indirectly affect other biological processes. While evidence of magnetism affecting human health is weak, similar experiments as this could prove to be another avenue for investigation.

"The joyous thing about this research is to see that the relationship between the spins of two individual electrons can have a major effect on biology," says Woodward.

Of course, birds aren't the only animal to rely on our magnetosphere for direction. Species of fish, worms, insects, and even some mammals have a knack for it. We humans might even be cognitively affected by Earth's faint magnetic field.

Evolution of this ability could have delivered a number of vastlydifferent actionsbased on different physics.

Having evidence that at least one of them connects the weirdness of the quantum world with the behaviour of a living thing is enough to force us to wonder what other bits of biology arise from the spooky depths of fundamental physics.

This research was published in PNAS.

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Birds Have a Mysterious 'Quantum Sense'. For The First Time, Scientists Saw It in Action - ScienceAlert

Jan 7th 2021

ALBERT EINSTEIN won the 1921 Nobel prize for physics in 1922. The temporal anomaly embodied in that sentence was not, alas, one of the counterintuitive consequences of his theories of relativity, which distorted accustomed views of time and space. It was down to a stubborn Swedish ophthalmologistand the fact that Einsteins genius remade physics in more ways than one.

The eye doctor was Allvar Gullstrand, one of the five members of the Nobel Committee for Physics charged with providing an annual laureate for the Swedish Royal Academy of Sciences to approve. Gullstrand thought Einsteins work on relativity an affront to common sense (which it sort of was) and wrong (which it really wasnt). Every year from 1918 on, the committee received more nominations for Einstein than for any other candidate. And every year, Gullstrand said no.

By 1921 the rest of the committee had had enough of settling for lesser laureates: the only decision which could be made unanimously was not to award the prize at all. Amid great embarrassment the academy chose to delay the 1921 prize until the following year, when it would be awarded in tandem with that of 1922. This gave Carl Wilhelm Oseen, a Swedish physicist newly appointed to the committee, time for a cunning plan. He nominated Einstein not for relativity, but for his early work explaining lights ability to produce electric currents. Though Gullstrand was still peeved, this carried the day. In November 1922 Einstein was awarded the 1921 prize for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect.

This adroit bit of face-saving also seems, a century on, fully justified. Einsteins first paper on the nature of light, published in 1905, contained the only aspect of his work that he himself ever referred to as revolutionary. It did not explain a new experiment or discovery, nor fill a gap in established theory; physicists were quite happy treating light as waves in a luminiferous aether. It simply suggested that a new way of thinking about light might help science describe the world more consistently.

That quest for consistency led Einstein to ask whether the energy in a ray of light might usefully be thought of as divided into discrete packets; the amount of energy in each packet depended on the colour, or wavelength, of the light involved. Thus the law mentioned in his Nobel citation: the shorter the wavelength of a beam of light, the more energy is contained in each packet.

Eight years earlier, in 1897, experiments carried out by J.J. Thompson had convinced his fellow physicists that the cathode rays produced by electrodes in vacuum tubes were made up of fundamental particles which he called electrons. Over time, Einsteins energy packets came to be seen as photons. The electron showed that electric charge was concentrated into point-like particles; the photon was a way of seeing energy as being concentrated in just the same way. Work by Einstein and others showed that the two particles were intimately involved with each other. To get energy into an electron, you have to use a photon; and when an electron is induced to give up energy, the result is a photon. This mutualism is embodied in some of todays most pervasive technologies; solar cells, digital cameras, fibre-optic datalinks, LED lighting and lasers. It is used to measure the cosmos and probe the fabric of space and time. It could yet send space probes to the stars.

The settled view of light which provided a context for Einsteins work dated from 1864, when James Clerk Maxwell rolled everything physics knew about electric and magnetic forces into a theory of electromagnetic fields produced by objects carrying an electric charge. Stationary charged objects created electric fields; those moving at a constant speed created magnetic fields. Accelerating charged objects created waves composed of both fields at once: electromagnetic radiation. Light was a form of such radiation, Maxwell said. His equations suggested there could be others. In the late 1880s Heinrich Hertz showed that was true by creating radio waves in his laboratory. As well as proving Maxwell right, he added the possibility of wireless telegraphy to the range of electrical technologiesfrom streetlights to dynamos to transatlantic telegraph cablesthat were revolutionising the late 19th century.

Scientists have since detected and/or made use of electromagnetic waves at wavelengths which range from many times the diameter of Earth to a millionth the diameter of an atomic nucleus. The wavelengths of visible light380 nanometres (billionths of a metre) at the blue end of the spectrum, 700nm at the red endare special only because they are the ones to which human eyes are sensitive.

The reason Einstein found what he called Maxwells brilliant discovery incomplete was that Maxwells fields were described, mathematically, as continuous functions: the fields strength had a value at every point in space and could not jump in value from one point to the next. But the material world was not continuous. It was lumpy; its molecules, atoms and electrons were separate entities in space. Physics described the material world through statistical accounts of the behaviour of very large numbers of these microscopic lumps; heat, for example, depended on the speed with which they vibrated or bumped into each other. It was a mathematical approach quite unlike Maxwells treatment of electromagnetic fields.

Yet matter and electromagnetic radiation were intimately associated. Every object emits electromagnetic radiation just by dint of having a temperature; its temperature is a matter of the jiggling of its constituent particles, some of which are charged, and the jiggling of charged particles produces electromagnetic waves. The spread of the wavelengths seen in that radiationits spectrumis a function of the bodys temperature; the hotter the body, the shorter both the median and highest wavelengths it will emit. The reason the human eye is sensitive to wavelengths in the 380-700nm range is that those are the wavelengths that a body gives off most prolifically if it is heated to 5,500C, the temperature of the surface of the Sun. They are thus the wavelengths that dominate sunlight (see chart).

If wavelengths and temperature were so intimately involved, Einstein believed, it had to be possible to talk about them in the same mathematical language. So he invented a statistical approach to the way entropya tendency towards disordervaries when the volume of a cavity filled with electromagnetic radiation changes. He then asked, in effect, what sort of lumpiness his statistics might be explaining. The answer was lumps of energy inversely proportional to the wavelength of the light they represented.

In 1905 Einstein was willing to go only so far as suggesting that this light-as-lump point of view provided natural-seeming explanations of various phenomena. Over subsequent years he toughened his stance. His work on relativity showed that Maxwells luminiferous aether was not required for the propagation of electromagnetic fields; they existed in their own right. His work on light showed that the energy in those fields could be concentrated into the point-like particles in empty space. Light was promoted from what he called a manifestation of some hypothetical medium into an independent entity like matter.

This account was not fully satisfying, because light was now being treated as a continuous wave in some contextswhen being focused by lenses, sayand as something fundamentally lumpy in others. This was resolved by the development of quantum mechanics, in which matter and radiation are both taken to be at the same time particulate and wavy. Part of what it is to be an electron, or a photon, or anything else is to have a wave function; the probabilities calculated from these wave functions offer the only access to truth about the particles that physics can have.

Einstein was never reconciled to this. He rejected the idea that a theory which provided only probabilities could be truly fundamental. He wanted a better way for a photon to be both wave and a particle. He never found it. All these 50 years of conscious brooding, he wrote to a friend in 1951, have brought me no nearer to the answer to the question, What are light quanta? Nowadays every Tom, Dick and Harry thinks he knows it, but he is mistaken.

Though Einstein was probably not thinking of him specifically, one of those Dicks was Richard Feynman, one of four physicists who, in the late 1940s, finished off the intellectual structure of which Einstein had laid the foundations: a complete theory of light and matter called quantum electrodynamics, or QED. It is a theory in which both matter and radiation are described in terms of fields of a fundamentally quantum nature. Particleswhether of light or matterare treated as excited states of those fields. No phenomenon has been found that QED should be able to explain and cannot; no measurement has been made that does not fit with its predictions.

Feynman was happy to forgo Einsteins brooding and straightforwardly assert that light is made of particles. His reasoning was pragmatic. All machines made to detect light will, when the light is turned down low enough, provide lumpy its-there-or-its-not readings rather than continuous ones. The nature of quantum mechanics and its wave functions mean that some of those readings will play havoc with conventional conceptions of what it is for a particle to be in a given place, or to exist as an independent entity. But that is just the way of the quantum, baby.

The precise manipulation of photons has shed much light on non-locality, decoherence and other strange quantum-mechanical phenomena. It is now making their application to practical problems, through quantum computation and quantum cryptography, increasingly plausible. But this Technology Quarterly is not about such quantum weirdness (for that, see our Technology Quarterly of January 2018). It is about how photons interactions with electrons have been used to change the world through the creation of systems that can turn light directly into electricity, and electricity directly into light.

That light and electricity were linked was known long before Einstein. In the 1880s Werner von Siemens, founder of the engineering firm that bears his name, attached the most far reaching importance to the mysterious photoelectric effect which led panels of selenium to produce trickles of current. Einsteins theory was taken seriously in part because it explained why a faint short-wavelength light could produce such a current when a bright longer-wavelength light could not: what mattered was the amount of energy in each photon, not the total number of photons.

Technology built on such ideas has since allowed light to be turned into electricity on a scale that would have boggled Siemenss mind. It lets billions of phone users make digital videos and send them to each other through an infrastructure woven from whiskers of glass. It lights rooms, erases tattoos, sculpts corneas and describes the world to driverless cars. Ingenuity and happy chance, government subsidies and the search for profit have created from Einsteins suggestion a golden age of lighta burst of innovation that, a century on, is not remotely over.

This article appeared in the Technology Quarterly section of the print edition under the headline "The liberation of light"

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How understanding light has led to a hundred years of bright ideas - The Economist

A multitasking nanomachine that can act as a heat engine and a refrigerator at the same time has been created by RIKEN engineers. The device is one of the first to test how quantum effects, which govern the behavior of particles on the smallest scale, might one day be exploited to enhance the performance of nanotechnologies.

Conventional heat engines and refrigerators work by connecting two pools of fluid. Compressing one pool causes its fluid to heat up, while rapidly expanding the other pool cools its fluid. If these operations are done in a periodic cycle, the pools will exchange energy and the system can be used as either a heat engine or a fridge.

It would be impossible to set up a macroscale machine that does both tasks simultaneouslynor would engineers want to, says Keiji Ono of the RIKEN Advanced Device Laboratory. Combining a traditional heat engine with a refrigerator would make it a completely useless machine, he says. It wouldnt know what to do.

But things are different when you shrink things down. Physicists have been developing ever smaller devices, sometimes based on single atoms. At these tiny scales, they have to account for quantum theorythe strange set of laws that says, for instance, an electron can exist in two places at the same time or have two different energies. Physicists are developing new theoretical frameworks and experiments to try to work out how such systems will behave.

The quantum version of the heat engine uses an electron in a transistor. The electron has two possible energy states. The team could increase or decrease the gap between these energy states by applying an electric field and microwaves. This can be analogous to the periodic expandingcompressing operation of a fluid in a chamber, says Ono, who led the experiment. The device also emitted microwaves when the electron went from the high-energy level to the lower one.

By monitoring whether the upper energy level was occupied, the team first demonstrated that the nanodevice could act as either a heat engine or as a refrigerator. But then they showed something far strangerthe nanomachine could act as both at the same time, which is a purely quantum effect. The researchers confirmed this by looking at the occupancy of the upper energy level, which combined to create a characteristic interference pattern. There was an almost perfect match between the experimental interference pattern and that predicted by theory, says Ono.

This may allow rapid switching between the two modes of operation, Ono explains. This ability could help create novel applications with such systems in the future.

Reference: Analog of a Quantum Heat Engine Using a Single-Spin Qubit by K. Ono, S.N. Shevchenko, T. Mori, S. Moriyama and Franco Nori, 15 October 2020, Physical Review Letters.DOI: 10.1103/PhysRevLett.125.166802

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Quantum Nanodevice Can Be Both a Heat Engine and Refrigerator at the Same Time - SciTechDaily

Jan 7th 2021

ALL THE technologies discussed in this report are moving forward apace. The companies which provide machinery to solar-cell manufacturers are ceaselessly trying to make more efficient use of silicon and less costly modules. In universities and elsewhere researchers are looking at ways to add a second layer to such cells so as to capture energy at wavelengths silicon ignoresthough their best attempts so far do not last very long outdoors.

Advances in manufacturing and design are making LEDs ever better sources of illumination. In more and more screens they backlight the liquid-crystal shutters which brighten pixels by detenebration. Some screens already do without shuttering, using liquid-crystal-free arrays of micro-LEDs to produce images that offer better contrast and use less energy. In information technology the division of labour that sees data processing done by electrons and data transmission by photons is under attack; switches that could be programmed to do some information processing while keeping that information in the form of photons would allow data to flow around data centres more quickly and efficiently. Laser beams of slightly different wavelengths are being packed ever more densely into optical fibres, with more bits encoded into every symbol stamped on to their light. The current record for data transfer down a single fibre, held by researchers at UCL, a British university, is 178 terabits a second.

But if you want to see lasers which push the boundaries of the possible in the most dramatic of ways, you have to turn to those made, not for practical applications, but to further science. Wherever researchers require ludicrous amounts of power or precision, theres every chance that they are using a laser, some sort of digital photon detector, or both. To see the cutting edge of what light can do, head for a lab.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California is a case in point: walking its halls evokes a sense of the technological sublime which is all but visceral. The 192 laser beams from the 100-metre-long, xenon-pumped beamlines that fill its two warehouse-sized clean rooms converge on a peculiarly perforated spherical chamber. When NIF is operational a tiny bubble at the centre of that chamber is illuminated with 500 terawatts, which is to say 500,000GW.

Given that the worlds total electricity generating capacity is less than 5TW, how is a 500TW system possible? The answer is brevity. Because power is energy divided by time, a relatively small amount of energy can provide a huge amount of power if it is delivered quickly enough. The NIF fires for only a few tens of nanoseconds (billionths of a second) at a time. Each blink-and-you-miss-it 500TW blast thus delivers only a kilowatt-hour or so of energy.

Using such a gargantuan device to provide such a modest amount of energy seems bizarre. But NIFs job requires the energy to be delivered with great spatial precision and almost instantaneously. Only then can it heat the lasers tiny targets to temperatures and pressures otherwise reached only in the centres of stars and the blasts of nuclear weaponsconditions which can fuse atomic nuclei. Congress paid billions for the NIF on the basis that it might open the way to making nuclear fusion of this sort a practical energy source. It has not delivered on those dreams. But it has provided new insights into astrophysics as well as experimental data relevant to the design and maintenance of hydrogen bombs, which is Lawrence Livermores main concern.

Physicists are not the only scientists entranced by lasers. One of the workhorses of genetic engineering is green fluorescent protein (GFP). The instructions for making GFP are easily added to genes for other proteins. When poked with finely focused lasers these modified proteins fluoresce, thus revealing their whereaboutsa handy way of learning which proteins cells put where.

A remarkable refinement of this technique, first demonstrated in 2011, is to turn the cell itself into a laser. Engineer a cell to produce GFP, put it between two mirrors and pump energy in and the proteins light will be amplified in just the same way as it would in a piece of ruby or neodymium-doped glass. Light-emission microscopy based on this possibility amplifies the light given off by fluorescent proteins and other light-emitting markers.

Photons can also be used to change how cells behave. By engineering proteins to be sensitive to light and then turning that light on and off, researchers can change what cells doincluding the ways they do, or dont, transmit nerve impulses. Laser light flashed on to the nerves of a suitably engineered flatworm, or shone down optical fibres into the brain of a mouse, allows researchers to turn different parts of the nervous system on and off and observe the changes in behaviour that follow. This optogenetic puppeteering provides all sorts of new insights into the machinery of the brain. With all due respect to those using photons to explore the strange interconnectedness of things in quantum mechanicswhich Einstein famously described as spookyphotons that can literally change a mind in mid-thought may be the spookiest of all.

The degree to which light-based techniques are changing sciences across the board can be seen in the past decades decisions by the Nobel Physics Committee. In 2014 the committee recognised a physical breakthrough in the production of lightthe development of blue LEDs, a technical tour de force which made the production of white light cheaper and easier than ever before. Since then the physics prize has been awarded to three different ways of using lasers either for experiments in the lab or observations of the world. A tour of these prize-winning accomplishments allows a last celebration of this golden age of light.

Start with pure power. A technique called chirped-pulse amplification, developed by Donna Strickland and Grard Mourou when they were both at the University of Rochester, allows lasers far more powerful than the NIFlasers which work in the petawatt range. It provides a way around the unfortunate fact that, above a certain power level, even a very short pulse will melt any laser trying to amplify it further. Chirp amplification solves the problem by stretching pulses out in both space and time. An intense packet of photons that is, say, a millimetre long, and thus passes through any machine in just three trillionths of a second, can be chirped into one that is a metre long and lasts a full three billionths of a second. This stretched pulse is low-power enough to be amplified, after which it can be compressed back into its original form as a burst just as short as ever but now containing many more photons.

Labs around the world now use this technique to produce bursts of light both far shorter and far more powerful than those at NIF using much cheaper equipment. This allows them to study nuclear processes that are even more extreme than fusion. If the pulses can be made 1,000 times shorter stillwhich Dr Mourou, at least, thinks is possible, given a decade or sothey could achieve something no other technology has yet managed: the creation of matter (and antimatter) from scratch.

Einsteins work dispensed with the need for an all-pervading luminiferous aether. But the fields evoked by quantum electrodynamics (QED), the mid-20th-century culmination of work on electromagnetism, quantum theory and relativity, populate empty space with something else instead: very faint possibilities. And QED says that, if light gets sufficiently intense, its photons will interact with these possibilities to bring forth brand new electrons from empty space. Einsteins insight that mass can be converted into energy has been proven many times, most terribly in nuclear weapons. Creating material particles from massless light alone would be a remarkable turning of the tables, and one that ought to provide new insight into the quantum fields involved.

After power, pressure. The momentum of photons is tiny; but when applied to tiny things it can do useful work. In the 1960s Arthur Ashkin of Bell Labs realised that, if a small transparent object is placed on the edge of a laser beam it will move to the beams centre (provided that the beam is brighter at the centre than the edge). This is because the photons that pass through the object have their path bent outward, away from the beam: conservation of momentum requires the object thus diverting them to move in the opposite direction. If, once caught up in the beam, the object strays from its bright centre, the light pressure will bring it back.

In the 1970s Dr Ashkin put this idea into practice, using laser beams as optical tweezers with which to manipulate microscopic beads. In the 1980s he got the technique to work on individual bacteria and virus particles, while his student Steven Chu used a variant to trap individual atomswork that won Dr Chu and colleagues a Nobel prize in 1997. The increasing use made of his tweezers in biology saw Dr Ashkin follow in his students footsteps in 2018, sharing the prize with Dr Strickland and Dr Mourou.

And then there is precision. Einsteins general theory of relativity, promulgated in 1915, explains gravity in terms of the distortions masses impose on spacetimespacetime being, to Einstein, simply the thing that clocks and rulers measure. His special theory of relativity had laid out the case for light being the ultimate ruler, a view that measurement professionals now share; the General Conference on Weights and Measures defines the metre not as the length of a specific rod in a vault in Paris, as it once did, but as the distance a photon in a vacuum travels in 1/299,792,458 of a second. Thus if you want to see ripples in spacetimesuch as those which relativity says must be produced when two very large masses pirouette around each otherlight is the best sort of ruler to use.

The Laser Interferometer Gravitational-wave Observatory (LIGO) consists of two such rulers. Its twin detectors, one in Louisiana and one in Washington state, both feature 4km-long perpendicular arms along which laser beams of truly phenomenal stability bounce back and forth (see chart). Instruments mounted at the point where the beams cross compare their phases in order to detect transitory differences in the arms lengths. Their precision is equivalent to that which would be needed to detect a hairs-breadth change in the distance to a nearby star.

On September 14th 2015 LIGO picked up the shiver in spacetime produced by the merger of two black holes 1.3bn light-years away. In 2017 the Nobel Physics Committee, free of naysaying ophthalmologists, awarded the prize to Rainer Weiss, Kip Thorne and Barry C. Barish, the three scientists who had done most to make that observation happen.

Their extraordinary measurement was treated, quite rightly, as a slightly late 100th-birthday present for Einsteins truly remarkable intellectual achievement. It was also an extraordinary demonstration of what can be done with photons. A century of work by scientists and engineers has taken the energy packets that Einstein first imagined in 1905 and produced a range of technologies with capabilities little short of the miraculousa collective achievement far greater than any single act of genius. Relativity is remarkable. Putting photons to use has been revolutionary.

This article appeared in the Technology Quarterly section of the print edition under the headline "New enlightenments"

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Illumination at the limits of knowledge - The Economist

Scientific articles in the field of physics are mostly very short and deal with a very restricted topic. A remarkable exception to this is an article published recently by physicists from the Universities of Mnster and Dsseldorf. The article is 127 pages long, cites a total of 1075 sources and deals with a wide range of branches of physics from biophysics to quantum mechanics.

Time axis showing the number of publications relating to dynamical density functional theory. Credit: M. te Vrugt et al.

The article is a so-called review article and was written by physicists Michael te Vrugt and Prof. Raphael Wittkowski from the Institute of Theoretical Physics and the Center for Soft Nanoscience at the University of Mnster, together with Prof. Hartmut Lwen from the Institute for Theoretical Physics II at the University of Dsseldorf. The aim of such review articles is to provide an introduction to a certain subject area and to summarize and evaluate the current state of research in this area for the benefit of other researchers.

In our case we deal with a theory used in very many areas the so-called dynamical density functional theory (DDFT), explains last author Raphael Wittkowski. Since we deal with all aspects of the subject, the article turned out to be very long and wide-ranging.

DDFT is a method for describing systems consisting of a large number of interacting particles such as are found in liquids, for example. Understanding these systems is important in numerous fields of research such as chemistry, solid state physics, or biophysics. This in turn leads to a large variety of applications for DDFT, for example in materials science and biology.

DDFT and related methods have been developed and applied by a number of researchers in a variety of contexts, says lead author Michael te Vrugt. We investigated which approaches there are and how they are connected and for this purpose we needed to do a lot of work acting as historians and detectives, he adds.

The article has been published in the journal Advances in Physics, which has an impact factor of 30.91 making it the most important journal in the field of condensed matter physics. It only publishes four to six articles per year. The first article on DDFT, written by Robert Evans, was also published in Advances in Physics, in 1979. This makes it especially gratifying that our review has also been published in this journal, says secondary author Hartmut Lwen. It deals with all the important theoretical aspects and fields of application of DDFT and will probably become a standard work in our field of research.

Reference: Classical dynamical density functional theory: from fundamentals to applications by Michael te Vrugt, Hartmut Lwen and Raphael Wittkowski, 20 December 2020, Advances in Physics.DOI: 10.1080/00018732.2020.1854965

The Wittkowski working group is being funded by the German Research Foundation DFG (WI 4170/3-1). The Lwen working group is also receiving financial support from the DFG (LO 418/25-1).

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Detective Work in Theoretical Physics: Comprehensive Review of Physics of Interacting Particles - SciTechDaily

Let's admit it: It's been a pretty rough year for our neck of the solar system. But it's been a great year for scientists studying more distant reaches of the universe. From a colossal explosion to mystery burps deciphered, here were some of the top stories in physics in 2020.

What might have been the universe's most powerful known explosion was detected back in 2016 but it really happened over 390 million years ago. While the first four-legged critters crawled onto land, a supermassive black hole in the Ophiuchus cluster launched a jet that blew a gargantuan cavity in the surrounding gas. In 2020, astronomers revisited the old data and realized just how powerful that explosion was: five times 10^54 joules of energy. For perspective, that's enough energy to literally rip apart all 300 billion stars in the Milky Way and a hundred more galaxies.

If you want to navigate among the stars, you're going to need a map. And that's exactly what the European Space Agency's Gaia space observatory created, using data on over 1.8 billion cosmic objects. The haul includes stars near and far, asteroids, comets and more. Want to know the position, velocity, spectrum and more for 0.5% of the population of our galaxy? You're in luck. Over 1,600 papers have already been published with Gaia data, and astronomers will be sure to mine the database for years to come. And here's the best part: There's even more data to come.

In 2020, the world lost one of its foremost and celebrated supersmart folks, Freeman Dyson. A man of unbounded imagination, he is perhaps best known in popular science circles for his conception of the Dyson sphere. (He didn't name it after himself; that came later.) A Dyson sphere is a hypothetical megastructure that completely encloses a star to harvest 100% of its solar energy exactly the energy a hyper-advanced civilization might need to do hyper-advanced things. So far, astronomers have not detected any Dyson spheres in our galaxy or any others, but Freeman's dream lives on.

It was too good to be true: claims of solid evidence for life in the cloud tops of Venus, an otherwise hellhole of a world. The reasoning was based on phosphine, a peculiar (and stinky) chemical emitted on Earth by anaerobic bacteria. To get as much phosphine in the atmosphere as was claimed, scientists proposed, Venus would need a large population of airborne microbes. Alas, further analysis reduced the observed amount of the stinky stuff (to levels barely considered noteworthy, let alone a sign for life), and in some analyses, removed it altogether as just another noisy signal. Don't worry, alien life: If you're out there, we'll keep looking.

Everyone loves a good fast radio burst (FRB), right? The source of these enigmatic, energetic signals has been an annoying puzzle to astronomers for more than a decade. FRBs are fast, high-powered, frequency-hopping radio signals coming from all over the sky, which makes it hard to pinpoint their origin. But finally, in 2020, astronomers got lucky: They found an FRB source in our own cosmic backyard. Follow-up observations revealed the culprit: an exotic star known as a magnetar (a super- magnetized dead stellar core). Apparently, magnetars sometimes burp out a tremendous amount of pent-up energy, which appears to Earthbound observers as a quick blast of radio emission.

Mars has liquid water. No, it's bone-dry. No, wait; it sometimes has water. No, nope, never mind. The Red Planet has been teasing astronomers for decades on the vital question of whether it's home to any liquid water at all. Astronomers care because, where there's water, there's a potential home for life. Earlier this year, astronomers claimed that there isn't just one, but four lakes of liquid water on Mars. The catch? They're incredibly salty more like a briny sludge than something to take a dip in and buried under a mile of frozen carbon dioxide at the southern polar cap. Not everybody is convinced, though, so don't pack your Martian swimsuit just yet.

2020 was surely the year of the solar system. Three independent spacecraft have successfully acquired samples and sent them on their way back to Earth. NASA launched its OSIRIS-REx mission to the asteroid Bennu, which collected so much material that its sample container leaked. The Japanese Hayabusa2 mission took a poke at the asteroid Ryugu and landed the material safely back to Earth. And the Chinese Chang'e 5 lander went on a mission to the moon, managing to launch a sample back to Earth before the lander broke down.

Astronomers have used gravitational waves (ripples in the fabric of space-time) to observe so many black hole collisions that by now, it's hardly newsworthy. But in 2020, astronomers announced the discovery of the biggest collision yet: a titanic merger of an 85-solar-mass black hole and a 66-solar-mass black hole. Post-merger, the resulting black hole tipped the scales at 142 times the mass of the sun. (About nine suns' worth of mass was converted into pure energy.) In other black hole news, the universe's ultimate Pandora's box was the subject of this year's Nobel Prize in physics.

Superconductors are super-neat. Due to the weirdness of quantum mechanics, under very special conditions, electrons can buddy up, with the pairs traveling together without losing energy. That means a game-changing technology where electricity can flow forever without resistance. Unfortunately, to make superconductors work, physicists have had to make everything super-cold. But in 2020, researchers announced the discovery of a superconductor at nearly room temperature, just 59 degrees Fahrenheit (15 degrees Celsius). The catch? You need to re-create the pressures found in Earth's center.

The novel coronavirus SARS-CoV-2 has devastated humanity, reaching pandemic levels in only a couple of months and washing across the globe. But we're fighting back with one of our most powerful weapons: vaccines. The current vaccines target a very specific part of the virus, a "spike" protein that it uses to invade our cells. One of the first steps in the war against COVID was to identify and map that protein, which researchers accomplished earlier this year, using a physics-based technique called cryogenic electron microscopy. Using this map, drugmakers could target this feature of the virus for vaccines to mimic, giving our immune systems a fighting chance.

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The 10 biggest physics stories of 2020 - Livescience.com

In popular culture, the physicist Erwin Schrdinger is most well known for his Schrdinger's cat thought experiment in which a cat exists in a closed box with a poison that has a 50/50 chance of killing it. At this moment, the cat is said to be both dead and alive at the same time. Thankfully, he did not actually subject cats to this, as it was merely a way to think about small particles like atoms, which are what quantum mechanics is all about.

Schrdinger's equation therefore looks at the probability that a particle is in a particular state, or, sticking with the cat, the probability that the cat is dead or alive. However, there's a gap of knowledge between that state of limbo and the moment when the particle is observed (aka when we find out the fate of the cat). The "many-worlds" theory supposes that all options do actually happen, sprouting off into different versions of the universe. There would then be a world where the cat is alive and one where it is dead. So, according to this complex physics theory, there is another world where the unsub's son isn't dead. However, sacrificing a bunch of people is not what's going to get him there.

Seasons 1 through 12 of Criminal Minds are available for streaming on Netflix, while the last three seasons may find their way there eventually.

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The Schrodinger Equation appears in Criminal Minds - Looper