Daily Archives: September 2, 2021

UNIVERSITY PARK, Pa. New experiments using trapped one-dimensional gases atoms cooled to the coldest temperatures in the universe and confined so that they can only move in a line fit with the predictions of the recently developed theory of generalized hydrodynamics. Quantum mechanics is necessary to describe the novel properties of these gases. Achieving a better understanding of how such systems with many particles evolve in time is a frontier of quantum physics. The result could greatly simplify the study of quantum systems that have been excited out of equilibrium. Besides its fundamental importance, it could eventually inform the development of quantum-based technologies, which include quantum computers and simulators, quantum communication, and quantum sensors. A paper describing the experiments by a team led by Penn State physicists appears Sept. 2 in the journal Science.

Even within classical physics, where the additional complexities of quantum mechanics can be ignored, it is impossible to simulate the motion of all the atoms in a moving fluid. To approximate these systems of particles, physicists use hydrodynamics descriptions.

The basic idea behind hydrodynamics is to forget about the atoms and consider the fluid as a continuum, said Marcos Rigol, professor of physics at Penn State and one of the leaders of the research team. To simulate the fluid, one ends up writing coupled equations that result from imposing a few constraints, such as the conservation of mass and energy. These are the same types of equations solved, for example, to simulate how air flows when you open windows to improve ventilation in a room.

Matter becomes more complicated if quantum mechanics is involved, as is the case when one wants to simulate quantum many-body systems that are out of equilibrium.

Quantum many-body systems which are composed of many interacting particles, such as atoms are at the heart of atomic, nuclear, and particle physics, said David Weiss, distinguished professor of physics at Penn State and one of the leaders of the research team. It used to be that except in extreme limits you couldnt do a calculation to describe out-of-equilibrium, quantum many-body systems. That recently changed.

The change was motivated by the development of a theoretical framework known as generalized hydrodynamics.

The problem with those quantum many-body systems in one dimension is that they have so many constraints on their motion that regular hydrodynamics descriptions cannot be used, said Rigol. Generalized hydrodynamics was developed to keep track of all those constraints.

Until now, generalized hydrodynamics had only previously been experimentally tested under conditions where the strength of interactions among particles was weak.

We set out to test the theory further, by looking at the dynamics of one dimensional gases with a wide range of interaction strengths, said Weiss. The experiments are extremely well controlled, so the results can be precisely compared to the predictions of this theory.

The research team uses one dimensional gases of interacting atoms that are initially confined in a very shallow trap in equilibrium. They then very suddenly increase the depth of the trap by 100 times, which forces the particles to collapse into the center of the trap, causing their collective properties to change. Throughout the collapse, the team precisely measures their properties, which they can then compare to the predictions of generalized hydrodynamics.

Our measurements matched the prediction of theory across dozens of trap oscillations, said Weiss. There currently arent other ways to study out-of-equilibrium quantum systems for long periods of time with reasonable accuracy, especially with a lot of particles. Generalized hydrodynamics allow us to do this for some systems like the one we tested, but how generally applicable it is still needs to be determined.

In addition to Weiss and Rigol, the research team includes Neel Malvania, Yicheng Zhang, and Yuan Le at Penn State; and Jerome Dubail at Universit de Lorraine in France. The research was funded by the U.S. National Science Foundation and the U.S. Army Research Office.

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Putting a new theory of many-particle quantum systems to the test | Penn State University - Penn State News

Like soft serve ice cream, beams of atoms and molecules now come with a swirl.

Scientists already knew how to dish up spiraling beams of light or electrons, known as vortex beams (SN: 1/14/11). Now, the first vortex beams of atoms and molecules are on the menu, researchers report in the Sept. 3 Science.

Vortex beams made of light or electrons have shown promise for making special types of microscope images and for transmitting information using quantum physics (SN: 8/5/15). But vortex beams of larger particles such as atoms or molecules are so new that the possible applications arent yet clear, says physicist Sonja Franke-Arnold of the University of Glasgow in Scotland, who was not involved with the research. Its maybe too early to really know what we can do with it.

In quantum physics, particles are described by a wave function, a wavelike pattern that allows scientists to calculate the probability of finding a particle in a particular place (SN: 6/8/11). But vortex beams waves dont slosh up and down like ripples on water. Instead, the beams particles have wave functions that move in a corkscrewing motion as a beam travels through space. That means the beam carries a rotational oomph known as orbital angular momentum. This is something really very strange, very nonintuitive, says physicist Edvardas Narevicius of the Weizmann Institute of Science in Rehovot, Israel.

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Narevicius and colleagues created the new beams by passing helium atoms through a grid of specially shaped slit patterns, each just 600 nanometers wide. The team detected a hallmark of vortex beams: a row of doughnut-shaped rings imprinted on a detector by the atoms, in which each doughnut corresponds to a beam with a different orbital angular momentum.

Another set of doughnuts revealed the presence of vortex beams of helium excimers, molecules created when a helium atom in an excited, or energized, state pairs up with another helium atom.

Next, scientists might investigate what happens when vortex beams of molecules or atoms collide with light, electrons or other atoms or molecules. Such collisions are well-understood for normal particle beams, but not for those with orbital angular momentum. Similar vortex beams made with protons might also serve as a method for probing the subatomic particles mysterious innards (SN: 4/18/17).

In physics, most important things are achieved when we are revisiting known phenomena with a fresh perspective, says physicist Ivan Madan of EPFL, the Swiss Federal Institute of Technology in Lausanne, who was not involved with the research. And, for sure, this experiment allows us to do that.

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New vortex beams of atoms and molecules are the first of their kind - Science News

August 30, 2021• Physics 14, 119

An innovative matter-wave lens exploiting atomic interactions is able to slow the expansion of a Bose-Einstein condensate in three dimensions, thus reaching unprecedented ultralow temperatures.

At ultralow temperatures, dilute atomic gases manifest their full quantum nature as matter waves in the form of Bose-Einstein condensates (BECs). Through the interference of matter waves in an interferometer, researchers can probe gravitational effects at microscopic scales and thereby test gravity at the quantum level. But improving the precision of these tests requires lowering the temperature of the BECs even further. Ernst Rasel from Leibniz University Hannover in Germany and colleagues have realized BECs at the lowest temperature so far (38 pK) by collimating the atoms in 3D with a new time-domain lens system based on atomic interactions [1].

The team prepared BEC matter waves with over one hundred thousand atoms and recorded their time evolution via absorption imaging during 2 s of free fall in a 110-m-high tower. Without any lensing applied, the BEC expanded through random thermal motion and became too dilute to be detected after 160 ms. In contrast, when the team collimated the atoms with their lens, the expansion slowed, and the BEC was visible throughout its fall. Moreover, the authors extrapolated their results and found that their innovative collimation technique can generate slowly expanding BECs that should remain detectable even after 17 s, which could be useful in future tests of gravity in space-based experiments.

BEC matter waves are a magnificent tool with which to explore the interface between quantum theory and general relativitythe underlying theories of the microcosmos and the macrocosmos, respectively. When a BEC is placed in an interferometer, its interference pattern will partly depend on gravitational effects due to the mass of the atoms. Detecting these effects could allow for fundamental tests, such as the verification of the Einstein equivalence principle with quantum objects. These tests require letting the BEC freely evolve for long times, which poses a problem, as the atoms tend to fly apart because of the internal kinetic energy (or temperature) of the system. Reducing this energy would extend the expansion time before the BEC becomes too dilute and improve the precision of matter-wave interferometry.

A powerful way to reduce a BECs internal kinetic energy is to exploit a matter-wave lens to focus the BEC atoms at infinity. Standard matter-wave lenses that are based on magnetic, optical, or electrostatic forces have indeed been used to reduce the BEC internal kinetic energy. Those tools can reach effective temperatures of about 50 pK but, unfortunately, only in two dimensions [2]. A magnetic lens, for example, has a cylindrical geometry that can bend the trajectory of atoms inward along the two radial directions, but it lacks this refractive power along the axial direction.

In their experiments, Rasel and colleagues achieve an unprecedently low temperature of 38 pK by exploiting an innovative matter-wave lens system in the time domain. Such a system can focus the BEC wave at infinity in all three spatial dimensions by cleverly combining both a magnetic lens and a collective-mode excitation (or shape vibration) in the BEC [3].

The team first generated a BEC of approximately one hundred thousand rubidium atoms within a cylindrically shaped magnetic trap produced on a microchip [4]. To excite the collective-mode oscillation, the researchers quickly reduced the trap magnetic bias field along one direction, while increasing the trapping strength in the other two directions. Because of the atomic interactions, the BEC responded by lengthening along its axis and slimming around the waist (Fig. 1). If allowed to continue this oscillation, the BEC would return to its original shape, but the researchers instead released the BEC at the time of maximum slimming. This was the key step for achieving 3D collimation, as it minimized the expansion along the axial direction. To slow the expansion around the BECs waist, the team applied a magnetic lens that collimated the atomic motion in the other two dimensions.

The experiments were performed at the Bremen drop tower in Germany, which provides an exceptional microgravity environment with residual accelerations of the order of 106g [5]. The researchers released the BEC at the top of the tower and measured its size via absorption imaging at different points during the free fall. From the data, they surmised that the expansion velocities were of the order of 60ms. In simulations, the team extended the free-fall time and showed that the BEC should remain detectable for up to 17 s.

By tuning both the oscillation time at the condensates release and the strength of the magnetic lenss potential, this new lensing method offers the possibility to engineer and control BEC shape and expansion for fundamental physics tests as well as for quantum sensing technologies. Indeed, the ability to generate slowly expanding BECs for tens of seconds can enable high-precision gravitational-wave detection [6], measurements of the gravitational constant [7] and the tidal force of gravity [8], as well as the search for ultralight dark matter [9] and a stringent quantum verification of Einsteins equivalence principle, both in drop towers and in space [10].

Furthermore, the 3D matter-wave lens system introduced by Rasel and co-workers provides a new and exciting perspective on the quantum advantage hidden behind the presence of interatomic interactions, often viewed as a drawback in matter-wave optics with long expansion times. Indeed, such interactions can be exploited as a powerful metrological tool in the development of matter-wave quantum sensors, enabling not only high-coherence properties but also highly nonclassical correlations.

Vincenzo Tamma is currently the Founding Director of the Quantum Science and Technology Hub and a reader in physics at the University of Portsmouth, UK, after being a group leader at the Institute of Quantum Physics at Ulm University, Germany. His Ph.D. research at the University of Maryland, Baltimore County and at the University of Bari Aldo Moro, Italy, was recognized with the Giampietro Puppi Award for the best Italian Ph.D. thesis in physics and astrophysics in 20072009. His research aims for a deeper understanding of the fundamental physics at the interface of quantum mechanics, quantum information, complexity theory, atomic physics, and general relativity, as well as at boosting the real-world implementation of quantum-enhanced technologies for computing and sensing applications.

Christian Deppner, Waldemar Herr, Merle Cornelius, Peter Stromberger, Tammo Sternke, Christoph Grzeschik, Alexander Grote, Jan Rudolph, Sven Herrmann, Markus Krutzik, Andr Wenzlawski, Robin Corgier, Eric Charron, David Gury-Odelin, Naceur Gaaloul, Claus Lmmerzahl, Achim Peters, Patrick Windpassinger, and Ernst M. Rasel

Phys. Rev. Lett. 127, 100401 (2021)

Published August 30, 2021

Researchers demonstrate lighter, smaller optics and vacuum components for cold-atom experiments that they hope could enable the development of portable quantum technologies. Read More

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Physics - 3D Collimation of Matter Waves - Physics

Left: The phase difference between |0| and exp(-iEt)|1| affords the total energy E . The curved arrow in purple indicates the phase evolution of | in time. Right: The phase difference between exp(-iE0t)|0|0 and exp(-iE1t)|1|1 affords the energy difference E1 E0, directly. The curved arrows in blue and in purple indicate the phase evolution of |0 and that of |1 , respectively. Credit: K. Sugisaki, K. Sato and T. Takui

Osaka City University creates a general quantum algorithm, executable on quantum computers, which calculates molecular energy differences without considering relevant total energies.

As newly reported by the journalPhysical Chemistry Chemical Physics, researchers from the Graduate School of Science at Osaka City University have developed a quantum algorithm that can understand the electronic states of atomic or molecular systems by directly calculating the energy difference in their relevant states. Implemented as a Bayesian phase different estimation, the algorithm breaks from convention by not focusing on the difference in total energies calculated from the pre- and post-phase evolution, but by following the evolution of the energy difference itself.

Almost all chemistry problems discuss the energy difference, not the total energy of the molecule itself, says research lead and Specially-Appointed Lecturer Kenji Sugisaki, also, molecules with heavy atoms that appear at the lower part of the periodic table have large total energies, but the size of the energy difference discussed in chemistry, such as electronic excitation states and ionization energies, does not depend much on the size of the molecule. This idea led Sugisaki and his team to implementing a quantum algorithm that directly calculates energy differences instead of total energies, creating a future where scalable or practical quantum computers enable us to carry out actual chemical research and materials development.

Currently, quantum computers are capable of performing the full configuration interaction (full-CI) calculations which afford optimal molecular energies with a quantum algorithm called quantum phase estimation (QPE), noting that the full-CI calculation for sizable molecular systems is intractable with any supercomputers. QPE relies on the fact that a wave function, | which denotes the mathematical description of the quantum state of a microscopic system in this case the mathematical solution of the Schrdinger equation for the microscopic system such as an atom or molecule time-evolutionally changes its phase depending on its total energy. In the conventional QPE, the quantum superposition state (|0|+|1|) 2 is prepared, and the introduction of a controlled time evolution operator makes | evolve in time only when the first qubit designates the |1 state. Thus, the |1 state creates a quantum phase of the post-evolution in time whereas the|0 state that of the pre-evolution. The phase difference between the pre- and post-evolutions gives the total energy of the system.

The researchers of Osaka City University generalize the conventional QPE to the direct calculation of the difference in the total energy between two relevant quantum states. In the newly implemented quantum algorithm termed Bayesian phase difference estimation (BPDE), the superposition of the two wave functions, (|0|0 + |1|1) 2, where |0 and |1 denote the wave function relevant to each state, respectively, is prepared, and the difference in the phase between |0 and |1 after the time evolution of the superposition directly gives the difference in the total energy between the two wave functions involved. We emphasize that the algorithm follows the evolution of the energy difference over time, which is less prone to noise than individually calculating the total energy of an atom or molecule. Thus, the algorithm suites the need for chemistry problems which require precise accuracy in energy. states research supervisor and Professor Emeritus Takeji Takui.

Previously, this research group developed a quantum algorithm that directly calculates the energy difference between electronic states (spin states) with different spin quantum numbers (K. Sugisaki, K. Toyota, K. Sato, D. Shiomi, T. Takui,Chem. Sci.2021,12, 21212132.). This algorithm, however, requires more qubits than the conventional QPE and cannot be applied to the energy difference calculation between the electronic states with equal spin quantum numbers, which is important for the spectral assignment of UV-visible absorption spectra. The BPDE algorithm developed in the study overcomes these issues, making it a highly versatile quantum algorithm.

Reference: A Bayesian phase difference estimation: a general quantum algorithm for the direct calculation of energy gaps 2 September 2021, Physical Chemistry Chemical Physics.

Other contributors include Kazuo Toyota, Kazunobu Sato and Daisuke Shiomi, all of whom are affiliated with the Department of Chemistry and Molecular Materials Science in Osaka City Universitys Graduate School of Science. Sugisaki is also affiliated with the Japan Science and Technology Agencys PRESTO Project, Quantum Software. Takui is also a University Research Administrator in the Research Support Department/University Research Administrator Center of Osaka City University.

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New Quantum Algorithm Directly Calculates the Energy Difference of Atoms and Molecules - SciTechDaily

We all carry around a little physics laboratory in our heads. As we move around the world climbing up stairs, lifting packages from Amazon, or riding our bicycles around corners we use that internal view of physics to give us our intuitive feeling for what the world is made out of and how it should behave. That is why it should come as something of a shock to learn how deeply and profoundly wrong that internal physics lab is about the fundamentals.

The world, fundamentally as seen through physics, is not how we imagine it to be from everyday experience. Nowhere is this failure of our internal physics labs more apparent than in the story of light and its wave-particle duality.

The question of exactly what kind of "thing" light is what we call its ontology dates to the beginning of modern physics. Both Descartes and Newton argued that every beam of light is really composed of tiny particles moving at high speed. The particles get emitted at the light's source (like the surface of the sun or the flame of a candle) and travel along straight line paths (except when bent by the influence of the medium through which they traveled) until they get absorbed by matter (like the retina of your eye).

Despite Newton's genius, others were not so convinced that light was made of particles. Around the same era as Newton, Christiaan Huygens proposed that light was really waves of energy moving through a background substrate or medium, just like waves moving through water or sound waves moving through air. When waves propagate across the ocean, for example, they do not carry individual water "particles" (that is, molecules) along with them from one place to another. Instead, the waves propagate through the water by sloshing H2O molecules back and forth as they pass.

Now, it is important to see how different the "particle" concept is from the "wave" concept for physicists. They are pretty much polar opposites, sort of like life vs. death, on vs. off, or pregnant vs. not pregnant. A particle is a little chunk of stuff that can only be in one place at one time (think bullets whizzing along a trajectory). A wave, however, is a distribution of energy that once emitted can spread out to fill space, being many places at once. Waves can also bend around objects as they travel. Bullets can only go through objects or be stopped by them.

While Newton's particle concept of light held sway for a while, by the end of the 1800s, waves had won out. James Clerk Maxwell developed a powerful theory predicting that light was nothing more than waves propagating through electromagnetic fields. Experiments confirmed Maxwell's predictions, opening the era of radio technology and many other applications. The mystery of light's ontology seemed to be solved.

Nature and light, however, had other ideas.

Credit: Davizro Photography via Adobe Stock and unlcepodger via Adobe Stock

Quantum mechanics, one of the greatest revolutions in physics, began with light. As physicists built new instruments probing the ever-smaller distances and timescales associated with atoms, they struggled to make sense of the interactions between matter and light. There was the "classical" view of electromagnetic waves getting emitted or absorbed by electrically charged particles of matter. But that theory failed spectacularly to explain what physicists were finding in their experiments. The math just did not work.

So, in a burst of creative desperation, physicists returned once again to imagining light as a particle. To explain what they saw in their atomic scale experiments, they built new models where light came in discrete bundles little packages or particles of light energy they called photons.

"But wait a minute!" you may be asking. What about all those experiments that showed light behaved like a wave, spreading out through space and bending around objects? Physicists could not ignore them any more than they could ignore their new studies that demanded light behave like particles.

Thus was born the now infamous wave-particle duality.

Rather than saying light really was a particle or it really was a wave, physicists adopted a new stance: it was both, and it was neither. If you performed an experiment looking for particle-like properties, light will show you those. But if you performed an experiment looking for wave-like properties, light will show you those, too. The only thing you could not do was look for both kinds of properties at the exact same time. And do not try to imagine light being some kind of merged entity like a "wavicle." Folks have tried that already and it has never worked.

Wave-particle duality was the beginning of a sea-change in how physics was done. Forced by experiments to become far more flexible in how they viewed reality, physicists began moving from easy-to-picture-in-your-head models to far more abstract, though still mathematically rigorous, views. Forget trying to picture what light is exactly like. That may or may not be possible.

Instead, imagination was propelled beyond "image," and the world was allowed to speak to us in new ways that still demanded reason in the form of mathematics but did not demand pictures. A century after the quantum revolution, we are still trying to understand what this wave-particle duality is really telling us.

What we can be sure of though is that the world is far weirder and more interesting than that little physics laboratory in our heads the ones based on everyday experience would have us believe.

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What is light? The limits and limitlessness of imagination - Big Think