Daily Archives: May 23, 2024

Phase-controlled projection measurement of quantum erasers for superresolution

Figure1 shows a universal scheme of the classically (coherently) excited superresolution based on phase-controlled quantum erasers. The superresolution scheme in Fig.1 originates in the Nth-order intensity correlations between phase-controlled quantum erasers, resulting in the PBW-like quantum feature11,25, as shown in Fig.2. Compared to the N=4 case11,25, the Inset of Fig.1 shows an arbitrary Nth-order superresolution scheme, where the first eight quantum erasers for N=8 are visualized with dotted blocks to explain the cascaded phase control of the quantum erasers using QWPs. For the quantum eraser, both single photon8 and cw laser light9 were experimentally demonstrated in a MachZehnder interferometer (MZI) for the polarization-basis projection onto a polarizer P. The MZI physics of coherence optics37 shows the same feature in both a single photon15 and cw light due to the limited Sorkin parameter, as discussed for the Born rule tests38. This originates in the equality between quantum and classical approaches for the first-order (N=1) intensity correlation24. Quantum mechanically, the deterministic feature of the MZI system is due to the double unitary transformation of a 50/50 nonpolarizing beam splitter (BS)1,15. The use of neutral density filters is not to generate single photons but to protect photodiodes from intensity saturation.

Schematic of a universal super-resolution based on phase-controlled quantum erasers. L: laser, ND: neutral density filter, H: half-wave plate, PBS: polarizing beam splitter, PZT: piezo-electric transducer, QWP: quarter-wave plate, P: polarizer, D: single photon (or photo-) detector, All rotation angles of Ps are at (uptheta =45^circ).

Numerical calculations of the Nth order intensity correlations in Fig.1. (upperleft) Individual first-order intensity correlation ({I}_{j}) in A, B, C, and D blocks. Blue star (circle): B3 (B4) in B, Cyan star (circle): C3 (C4) in C, Red star (circle): A3 (A4) in A, Magenta star (circle): D3 (D4) in D. (upper right) Second-order intensity correlation in each block of the Inset of Fig. 1.(lower right) Fourth-order intensity correlation between (red) A and B, and (blue) C and D. (lowerleft) Eight-order intensity product between all quantum erasers. ({I}_{K}={I}_{K1}{I}_{K2}) (K=A, B, C, D), ({I}_{AB}^{(4)}={I}_{A}^{(2)}{I}_{B}^{(2)}), ({I}_{CD}^{(4)}={I}_{C}^{(2)}{I}_{D}^{(2)}), and ({I}_{ABCD}^{(8)}={I}_{AB}^{(4)}{I}_{CD}^{(4)}). ({xi }_{A}=frac{pi }{2}), ({xi }_{C}=frac{pi }{4}), and ({xi }_{D}=frac{3pi }{4}).

The rotation angle of QWP in each block of the quantum erasers in the Inset of Fig.1 is to induce a phase gains (({xi }_{j})) to the vertical component of the corresponding light37. As experimentally demonstrated25, the QWP induces a phase delay to the vertical polarization component compared to the horizontal one37. This polarization-basis-dependent phase gain of the light directly affects the quantum eraser via polarization-basis projection measurements, resulting in a fringe shift11,25, because the role of the polarizer P is to project orthogonal polarization bases onto the common axis (widehat{{text{p}}}) (see Eqs. (2)(8))8,9,18. The random path length to the polarizer from PBS in Fig.1 does not influence the intensity correlations due to the unaffected global phase by the Born rule, where intensity (measurement) is the absolute square of the amplitude13,14. Thus, controlling the QWP of each block makes an appropriate fringe shift of the quantum erasers for the first-order intensity products.

In the proposed universal scheme with a practically infinite number of phase-controlled quantum erasers in Fig.1, a general coherence solution of the phase-controlled superresolution is coherently derived from the combinations of QWPs (see Eq.(25) and Figs. 2 and 3). Then, the general solution is compared with PBWs based on N00N states for the discussion of phase quantization of the Nth-order intensity product in Fig.4. Such phase quantization has already been separately discussed for coherence de Broglie waves (CBWs) in a coupled MZI system for the wave nature of quantum mechanics39,40. Unlike CBWs resulting from MZI superposition, the present phase quantization of superresolution is for the intensity product between phase-controlled quantum erasers. On the contrary to energy quantization of the particle nature in quantum mechanics1, the phase quantization is for the wave nature, where the particle and wave natures are mutually exclusive.

Numerical calculations for the normalized Kth-order intensity products. K represents the number of quantum erasers used for intensity product measurements.

Phase quantization of the intensity products in Fig.3. K is the order of intensity product. Dotted: K=1, Cyan: K=2, Blue: K=4, Red: K=8.

A coherence approach based on the wave nature of a photon is adopted to analyze Fig.1 differently from the quantum approach based on quantum operators1,26,27,28,29,30,31,32,33. The novel feature of the present method is to use common intensity products of cw lights via polarization-basis projection of the phase-controlled quantum erasers. Thus, there is no need for single-photon coincidence detection. Instead, the intensity product is enough for a single shot measurement, as is in nonlinear optics. Technically, the condition ({text{N}}le {text{M}}) is required, where N and M are the number of quantum erasers used for the intensity product and the photon number of the input light, respectively. Here it should be noted that both intensity product and coincidence detection are effective within the ensemble coherence time of the input light L. In that sense, a pulsed laser is more appropriate for the use of a time-bin scheme as shown for quantum key distribution41.

The amplitude of the output field of the Michelson interferometer in Fig.1 is represented using the BS matrix representation42as:

$${{varvec{E}}}_{A}=frac{i{E}_{0}}{sqrt{2}}left(widehat{H}{e}^{ivarphi }+widehat{V}right)$$

(1)

where ({E}_{0}) is the amplitude of the light just before entering the Michelson interferometer. (widehat{H}) and (widehat{V}) are unit vectors of horizontal and vertical polarization bases of the light, respectively. In Eq.(1), the original polarization bases are swapped by the 45 rotated QWPs inserted in both paths for full throughput to the ({E}_{A}) direction. Due to the orthogonal bases, Eq.(1) results in no fringe, satisfying the distinguishable photon characteristics of the particle nature in quantum mechanics: (langle {I}_{A}rangle ={I}_{0}).

By the rotated polarizers in Fig.1, whose rotation angle (uptheta) is from the horizontal axis, Eq.(1) is modified for the split quantum erasers:

$${{varvec{E}}}_{A1}=frac{i{E}_{0}}{sqrt{2}sqrt{8}}left(costheta {e}^{ivarphi }+sintheta {e}^{i{xi }_{A}}right)widehat{p}$$

(2)

$${{varvec{E}}}_{A2}=frac{-{E}_{0}}{sqrt{2}sqrt{8}}left(-costheta {e}^{ivarphi }+sintheta {e}^{i{xi }_{A}}right)widehat{p}$$

(3)

$${{varvec{E}}}_{B1}=frac{-i{E}_{0}}{sqrt{2}sqrt{8}}left(costheta {e}^{ivarphi }+sintheta right)widehat{p}$$

(4)

$${{varvec{E}}}_{B2}=frac{-i{E}_{0}}{sqrt{2}sqrt{8}}left(-costheta {e}^{ivarphi }+sintheta right)widehat{p}$$

(5)

$${{varvec{E}}}_{C1}=frac{-{E}_{0}}{sqrt{2}sqrt{8}}left(costheta {e}^{ivarphi }+sintheta {e}^{i{xi }_{C}}right)widehat{p}$$

(6)

$${{varvec{E}}}_{C2}=frac{-i{E}_{0}}{sqrt{2}sqrt{8}}left(-costheta {e}^{ivarphi }+sintheta {e}^{i{xi }_{C}}right)widehat{p}$$

(7)

$${{varvec{E}}}_{D1}=frac{-i{E}_{0}}{sqrt{2}sqrt{8}}left(costheta {e}^{ivarphi }+sintheta {e}^{i{xi }_{D}}right)widehat{p}$$

(8)

$${{varvec{E}}}_{D2}=frac{{E}_{0}}{sqrt{2}sqrt{8}}left(-costheta {e}^{ivarphi }+sintheta {e}^{i{xi }_{D}}right)widehat{p}$$

(9)

where (widehat{p}) is the axis of the polarizers, and (sqrt{8}) is due to the eight divisions (N=8) of ({{varvec{E}}}_{A}) by the lossless BSs. In Eqs. (2)(9), the projection onto the polarizer results in (widehat{H}to costheta widehat{p}) and (widehat{V}to sintheta widehat{p}). By BS, the polarization direction of (widehat{H}) is reversed, as shown in the mirror image37. By the inserted QWP in each block, the ({xi }_{j})-dependent phase gain is to the (widehat{V}) component only37. As demonstrated for the projection measurement of N interfering entangled photons23,29, the Nth-order intensity correlation is conducted by the N split ports in the Inset of Fig.1.

Thus, the corresponding mean intensities of all QWP-controlled quantum erasers in the Inset of Fig.1 are as follows for (uptheta =45^circ) of all Ps:

$$langle {I}_{A1}rangle =frac{{I}_{0}}{2N}langle 1+{{cos}}(varphi -{xi }_{A})rangle$$

(10)

$$langle {I}_{A2}rangle =frac{{I}_{0}}{2N}langle 1-{{cos}}(varphi -{xi }_{A})rangle$$

(11)

$$langle {I}_{B1}rangle =frac{{I}_{0}}{2N}langle 1+cosvarphi rangle$$

(12)

$$langle {I}_{B2}rangle =frac{{I}_{0}}{2N}langle 1-cosvarphi rangle$$

(13)

$$langle {I}_{C1}rangle =frac{{I}_{0}}{2N}leftlangle 1+{cos}(varphi -{xi }_{C})rightrangle$$

(14)

$$langle {I}_{C2}rangle =frac{{I}_{0}}{2N}leftlangle 1-{cos}(varphi -{xi }_{C})rightrangle$$

(15)

$$langle {I}_{D1}rangle =frac{{I}_{0}}{2N}leftlangle 1+{cos}(varphi -{xi }_{D})rightrangle$$

(16)

$$langle {I}_{D2}rangle =frac{{I}_{0}}{2N}leftlangle 1-{cos}(varphi -{xi }_{D})rightrangle$$

(17)

Equations(10)(17) are the unveiled quantum mystery of the cause-effect relation of the quantum eraser found in the ad-hoc polarization-basis superposition via the polarization projection onto the (widehat{p}) axis of the polarizer. The price to pay for this quantum mystery is 50% photon loss by the polarization projection11,22, regardless of single photons8 or cw light9. By adjusting ({xi }_{j}) of QWP in each block, appropriate fringe shifts of the quantum erasers can also be made accordingly, as shown in Fig.2 for ({xi }_{A}=frac{pi }{2}), ({xi }_{C}=frac{pi }{4}), and ({xi }_{D}=frac{3pi }{4}).

The corresponding second-order (N=2) intensity correlations between the quantum erasers in each block is directly obtained from Eqs. (10)(17) for ({xi }_{A}=frac{pi }{2}), ({xi }_{C}=frac{pi }{4}), and ({xi }_{D}=frac{3pi }{4}):

$$leftlangle {{text{I}}}_{A1A2}^{(2)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{2}leftlangle {sin}^{2}left(varphi -frac{pi }{2}right)rightrangle$$

(18)

$$leftlangle {{text{I}}}_{B1B2}^{(2)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{2}leftlangle {sin}^{2}varphi rightrangle$$

(19)

$$leftlangle {{text{I}}}_{C1C2}^{(2)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{2}leftlangle {sin}^{2}left(varphi -frac{pi }{4}right)rightrangle$$

(20)

$$leftlangle {{text{I}}}_{D1D2}^{(2)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{2}leftlangle {sin}^{2}left(varphi -frac{3pi }{4}right)rightrangle$$

(21)

where the second-order intensity fringes are also equally shifted as in the first-order fringes (see Fig.2). Likewise, the fourth-order (N=4) intensity correlations between any two blocks can be derived from Eqs. (18)(21) as:

$$leftlangle {{text{I}}}_{A1A2B1B2}^{(4)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{4}leftlangle {sin}^{2}varphi {sin}^{2}left(varphi -frac{pi }{2}right)rightrangle$$

(22)

$$leftlangle {{text{I}}}_{C1C2D1D2}^{(4)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{4}leftlangle {sin}^{2}left(varphi -frac{pi }{4}right){sin}^{2}left(varphi -frac{3pi }{4}right)rightrangle$$

(23)

Thus, the eighth-order (N=8) intensity correlation for all quantum erasers in the Inset of Fig.1 is represented as:

$$leftlangle {{text{I}}}_{A1A2B1B2C1C2D1D2}^{(8)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{8}leftlangle {sin}^{2}varphi {sin}^{2}left(varphi -frac{pi }{4}right){sin}^{2}left(varphi -frac{pi }{2}right){sin}^{2}left(varphi -frac{3pi }{4}right)rightrangle$$

(24)

From Eq.(24), the proposed scheme of superresolution for N=8 is analytically confirmed for the satisfaction of the Heisenberg limit in quantum sensing (see Figs. 2 and 3).

Figure2 shows numerical calculations of the Nth-order intensity correlations using Eqs. (10)(17) for ({xi }_{A}=uppi /2), ({xi }_{C}=uppi /4), and ({xi }_{D}=3uppi /4) to demonstrate the proposed PBW-like superresolution using phase-controlled coherent light in Fig.1. From the upper-left panel to the clockwise direction in Fig.2, the simulation results are shown for ordered (N=1, 2, 4, 8) intensity correlations. As shown, all ordered-intensity correlations are equally spaced in the phase domain, where the pair of quantum erasers in each block satisfies the out-of-phase relation (see the same colored o and * curves in the upper-left panel). Thus, the higher-order intensity correlation between blocks also results in the same out-of-phase relation, as shown for N=2 and N=4, resulting in the Heisenberg limit, (mathrm{delta varphi }=uppi /{text{N}}).

For an arbitrary order N, the jth block with ({xi }_{j})-QWP can be assigned to the universal scheme of the phase-controlled superresolution. For the expandable finite block series with ({xi }_{j})-phase-controlled quantum erasers in Fig.1, the generalized solution of the kth-order intensity correlation can be quickly deduced from Eq.(24):

$$leftlangle {{text{I}}}^{(K)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{K}leftlangle prod_{j=0}^{K}{sin}^{2}(varphi -{xi }_{j})rightrangle$$

(25)

where ({xi }_{j}=j2pi /N) and ({text{K}}le {text{N}}). Unlike the N00N-based superresolution in quantum sensing26,27,28,29,30,31, the kth-order intensity product in Eq.(25) can be coherently amplified as usual in classical (coherence) sensors. Thus, the reduction by ({left(frac{{I}_{0}}{2N}right)}^{k}) has no critical problem for potential applications of the proposed superresolution.

Figure3 is for the details of numerical calculations for K=1,2,...,8 and K=80 using Eq.(25). The top panels of Fig.3 are for odd and even Ks, where the fringe number linearly increases as K increases, satisfying the Heisenberg limit31. For the K-proportional fringe numbers, the positions of the first fringes for K=1,2,...,8 move from (uppi /2) for K=1 (black dot, left panel) to (uppi /16) for K=8 (blue dot, middle panel). As in PBWs, thus, the same interpretation of the K-times increased effective frequency to the original frequency of the input light can be made for the Kth-order intensity correlations. Unlike N00N state-based PBWs, the intensity-product order can be post-determined by choosing K detectors out of N quantum erasers.

The right panel of Fig.3 is for comparison purposes between K=8 and K=80, where the resulting ten times increased fringe numbers indicate ten times enhanced phase resolution, satisfying the Heisenberg limit. Thus, the pure coherence solution of the PBW-like quantum feature satisfying the Heisenberg limit is numerically confirmed for the generalized solution of Eq.(25). Here, the coincidence detection in the particle nature of quantum sensing with N00N states is equivalent to the coherence intensity-product measurement, where the coherence between quantum erasers is provided by the cw laser L within its spectral bandwidth. Furthermore, the ({xi }_{j}) relation between blocks composed of paired quantum erasers may imply the phase relation between paired entangled photons (discussed elsewhere).

Figure4 discusses the perspective of the phase-basis relation provided by ({xi }_{j}) in Eq.(25) for the Kth-order intensity correlations of the proposed superresolution. From the colored dots representing the first fringes of the ordered intensity products, the generalized phase basis of the Kth-order intensity correlation can be deduced for ({mathrm{varphi }}_{K}=uppi /{text{K}}). Thus, the Kth-order intensity correlation behaves as a K-times increased frequency ({f}_{K} (=K{f}_{0})) to the original input frequency ({f}_{0}) of L. The intensity-order dependent effective frequency ({f}_{K}) is equivalent to the PBW of the N00N state in quantum metrology26,27,28,29,30,31,32.

Based on the K-times increased fringes in the Kth-order intensity product, the numerical simulations conducted in Fig.4 can be interpreted as phase quantization of the intensity products through projection measurements of the quantum erasers. As shown in the PBW-like quantum features, these discrete eigenbases of the intensity products can also be compared to a K-coupled pendulum system43, where the phase quantization in Fig.4 can be classically understood39,40. Unlike the N-coupled pendulum system43 or CBWs from MZI interference39,40, however, any specific mode of ({varphi }_{K}) can be deterministically taken out by post-selection of a particular number of blocks used for the intensity-product order K in Fig.1. Like the energy quantization of the particle nature in quantum mechanics, thus, Fig.4 is another viewpoint of the wave nature for the proposed superresolution. By the wave-particle duality in quantum mechanics, both features of the energy and phase quantization are mutually exclusive.

From the universal scheme of the superresolution based on the phase-controlled quantum erasers in Fig.1, a generalized solution of the Kth-order intensity correlation in Fig.4 can also be intuitively obtained:

$$leftlangle {{text{I}}}_{{P}_{1}{P}_{2}dots {P}_{j}dots {P}_{K/2}}^{(K)}(0)rightrangle ={left(frac{{I}_{0}}{2N}right)}^{K}leftlangle {sin}^{2}(Kvarphi /2)rightrangle$$

(26)

where ({P}_{j}={Z}_{1}{Z}_{2}), and ({Z}_{j}) is the jth quantum eraser of the P block. Here, the effective phase term (Kvarphi) in Eq.(26) represents the typical nonclassical feature of PBWs used for quantum sensing with N00N states 30,31. The numerical simulations of Eq.(26) for N=1, 2, 4, and 8 perfectly match those in Fig.4 (not shown). Although the mathematical forms between Eqs. (25) and (26) are completely different, their quantum behaviors are the same as each other. Thus, Eq.(26) is equivalent to the superresolution in Eq.(25) 13,25, where the phase quantization is accomplished by ordered intensity products of the divided output fields of the Michelson interferometer. Unlike coincidence detection between entangled photons under the particle nature26,27,28,29,30,31,32, the present coherence scheme with the wave nature is intrinsically deterministic within the spectral bandwidth of the input laser. Thus, the coincidence detection in N00N-based quantum sensing is now replaced by the intensity product between independently phase-controlled quantum erasers using QWPs. Such a coherence technique of the individually and independently controlled quantum erasers can be applied for a time-bin scheme with a pulsed laser, where intensity products between different time bins are completely ignored due to their incoherence feature41.

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Coherently excited superresolution using intensity product of phase-controlled quantum erasers via polarization-basis ... - Nature.com

CAMBRIDGE, Mass. Could moving atoms closer together than ever before open the door to the next quantum breakthrough? Physicists at the Massachusetts Institute of Technology have developed a new technique that allows them to arrange atoms in two distinct layers separated by a mere 50 nanometers about 2,000 times thinner than a human hair. This monumental achievement opens up exciting possibilities for studying exotic quantum phenomena and developing novel technologies.

The study, published in Science andled by Professor Wolfgang Ketterle, used laser light to trap and cool dysprosium atoms to ultra-low temperatures near absolute zero. At these extreme conditions, the atoms behave more like waves than particles, enabling researchers to manipulate them with exquisite precision.

Imagine a pair of invisible sheets, each made up of a single layer of atoms. Now, picture bringing those sheets so close together that theyre almost touching, but not quite. Thats essentially what the MIT scientists have accomplished, except on a scale so tiny its difficult to wrap your head around.

To put it in perspective, if an atom were the size of a marble, the two layers would be separated by just a few inches. But because atoms are so incredibly small, the actual distance between the layers is only 50 nanometers. Thats like taking two pieces of paper and holding them apart with a single strand of spider silk.

We have gone from positioning atoms from 500 nanometers to 50 nanometers apart, and there is a lot you can do with this, says Wolfgang Ketterle, the John D. MacArthur Professor of Physics at MIT, in a media release. At 50 nanometers, the behavior of atoms is so much different that were really entering a new regime here.

Creating these atomic bilayers required a clever trick. The researchers used two different colors of laser light, each one specifically tuned to interact with atoms in a particular quantum state, or energy level. Its a bit like having two TV remote controls, one for each layer of atoms. By carefully adjusting the laser beams, they were able to trap the atoms and move them around with nanometer precision.

What makes this setup truly special is the way the atoms in the two layers interact with each other. Even though theyre not physically touching, the atoms can still feel each others presence through a peculiar force called dipolar interaction. Its similar to how two tiny bar magnets would attract or repel each other, even from a short distance.

In the atomic realm, these dipolar interactions can give rise to all sorts of strange and wonderful behaviors. For example, the researchers observed that the atoms in one layer could actually talk to the atoms in the other layer and exchange energy, almost like they were engaged in a microscopic game of telephone. This phenomenon, known as sympathetic cooling, could potentially be used to build ultra-efficient refrigerators for cooling down quantum computers.

But the most exciting possibilities lie in the realm of fundamental physics. By studying how atoms behave in these closely spaced bilayers, scientists hope to gain new insights into exotic states of matter like superfluids and quantum magnets. These materials have properties that seemingly defy the laws of classical physics, such as the ability to flow without friction or resist changes in magnetic fields.

Down the road, the atomic bilayer setup could also be used as a platform for developing quantum technologies, such as ultra-precise sensors, secure communication networks, and powerful computers that can solve problems beyond the reach of any classical machine. Its a bit like having a miniature quantum playground where scientists can tinker with the building blocks of matter and see what new gadgets they can dream up.

Of course, theres still a lot of work to be done before these applications become a reality. The MIT team plans to conduct more experiments to better understand the subtle dance of dipolar interactions between the atomic layers. They also want to explore what happens when the atoms are cooled down even further to temperatures so low that quantum effects completely take over.

But even at this early stage, the results are nothing short of remarkable. By pushing the boundaries of atomic manipulation, these researchers have given us a glimpse into a world thats both strangely familiar and utterly alien a world where the rules of quantum mechanics reign supreme, and the line between science and science fiction starts to blur.

As we continue to explore this strange and wonderful frontier, one thing is clear: the future of physics is looking brighter than ever, and it all starts with a humble pair of atomic sheets, separated by a distance so small its almost hard to believe. But in the grand scheme of things, that tiny gap might just be the key to bridging the gap between the world we know and the one weve only begun to imagine.

StudyFinds Editor-in-ChiefSteve Fink contributedto this report.

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Scientists move atoms so close together it may change quantum physics forever - - Study Finds

Pan, a professor of modern physics and executive vice-president at the University of Science and Technology of China (USTC), has done pioneering work in multi-article interferometry and quantum experiments in space, the societys Fellows Directory says.

It also praises his team for having closed major loopholes for secure quantum communication associated with imperfect devices, making it a viable technology under realistic conditions.

Pan also featured on the 2017 Natures 10, the premier magazines annual list of the people who matter most in science. He had lit a fire under Chinas quantum technology efforts since returning full-time in 2008 after training in Europe, Nature said, labelling Pan as a physicist who took quantum communication to space and back.

In 2016, under Pans leadership, China launched the worlds first quantum science space satellite, Micius, with a mission to establish a secure communication line between China and Europe, a fact mentioned also in the Royal Society directory.

The Royal Society bio also lauded Pan for his achievements in quantum computing technology. His team demonstrated quantum computational advantage, validating the feasibility of quantum computing systems to outperform classical machines in solving specific problems, his bio says.

The breakthroughs made by Pans USTC team are often reported by top academic journals.

Pan is also an academician of the Chinese Academy of Sciences (CAS), Chinas premier research institute, and is director of the CAS Centre for Excellence in Quantum Information and Quantum Physics in Anhui province, where he is based with the USTC.

The USTC is not only home to leading quantum physicists such as Pan, but also an innovation hub that has spawned many start-ups, thanks to steady scientific breakthroughs, a competitive talent pool and generous local government support.

The Royal Society, formally the Royal Society of London for Improving Natural Knowledge, was founded in 1660 and is the worlds oldest continuous scientific academy.

In 2022, George Gao Fu, then head of the Chinese Centre for Disease Control and Prevention, a leading scientist in the field of virology and immunology, was elected by the society for his contribution to the fight against the Covid-19 pandemic.

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Chinas father of quantum named Royal Society fellow as US targets sector - South China Morning Post

In the realm of quantum physics, proximity plays a crucial role. As atoms interact more strongly when they are positioned closely together, scientists have long sought ways to arrange them as tightly as possible in quantum simulators.

These simulators allow researchers to explore exotic states of matter and build novel quantum materials. However, there has been a limit to how close atoms could be positioneduntil now.

Typically, scientists cool the atoms to a stand-still and use laser light to arrange them, but the wavelength of light has restricted the minimum distance between particles to around 500 nanometers.

Now, a team of physicists at MIT has developed a breakthrough technique that enables them to position atoms a mere 50 nanometers apart. To put this into perspective, a red blood cell measures about 1,000 nanometers in width.

The MIT team, led by Wolfgang Ketterle, the John D. MacArthur Professor of Physics, demonstrated their new approach using dysprosium, the most magnetic atom in nature.

By manipulating two layers of dysprosium atoms and precisely positioning them 50 nanometers apart, they observed magnetic interactions 1,000 times stronger than if the layers were separated by the previous limit of 500 nanometers.

We have gone from positioning atoms from 500 nanometers to 50 nanometers apart, and there is a lot you can do with this, says Ketterle. At 50 nanometers, the behavior of atoms is so much different that were really entering a new regime here.

Furthermore, the researchers were able to measure two new effects caused by the atoms proximity: thermalization, where heat transfers from one layer to another, and synchronized oscillations between the layers. These effects diminished as the layers were spaced farther apart.

Conventional techniques for manipulating and arranging atoms have been limited by the wavelength of light, which typically stops at 500 nanometers. This optical resolution limit has prevented scientists from exploring phenomena that occur at much shorter distances.

Conventional techniques stop at 500 nanometers, limited not by the atoms but by the wavelength of light, explains Ketterle. We have found now a new trick with light where we can break through that limit.

The teams innovative approach begins by cooling a cloud of atoms to about 1 microkelvin, just above absolute zero, causing the atoms to come to a near-standstill.

They then use two laser beams with different frequencies and circular polarizations to create two groups of atoms with opposite spins.

Each laser beam forms a standing wave, a periodic pattern of electric field intensity with a spatial period of 500 nanometers.

By tuning the lasers such that the distance between their respective peaks is as small as 50 nanometers, the atoms gravitating to each lasers peaks are separated by the same distance.

To achieve this level of precision, the lasers must be extremely stable and resistant to external noise. The team realized they could stabilize both lasers by directing them through an optical fiber, which locks the light beams in place relative to each other.

The idea of sending both beams through the optical fiber meant the whole machine could shake violently, but the two laser beams stayed absolutely stable with respect to each others, says lead author and physics graduate student Li Du.

By applying their technique to dysprosium atoms, the researchers observed two novel quantum phenomena at the extremely close proximity of 50 nanometers.

First is collective oscillation, where vibrations in one layer caused the other layer to vibrate in sync. Next is thermalization, where one layer transferred heat to the other purely through magnetic fluctuations in the atoms.

Until now, heat between atoms could only by exchanged when they were in the same physical space and could collide, notes Du. Now we have seen atomic layers, separated by vacuum, and they exchange heat via fluctuating magnetic fields.

The teams results introduce a new technique that can be applied to many other atoms to study quantum phenomena.

They believe their approach can be used to manipulate and position atoms into configurations that could generate the first purely magnetic quantum gate.

This would be a key building block for a new type of quantum computer.

We are really bringing super-resolution methods to the field, and it will become a general tool for doing quantum simulations, says Ketterle. There are many variants possible, which we are working on.

In summary, the MIT teams pioneering technique opens up a new frontier in quantum physics, enabling scientists to explore previously inaccessible phenomena and build novel quantum materials.

By positioning atoms a mere 50 nanometers apart, they have unlocked a realm where magnetic interactions reign supreme and quantum effects emerge in stunning clarity.

As researchers continue to refine and expand upon this approach, they inch closer to the development of purely magnetic quantum gates and the realization of cutting-edge quantum computers.

The future of quantum simulations looks brighter than ever, and the possibilities are limited only by the imagination of the scientists who dare to push the boundaries of what is possible.

The studys co-authors include Pierre Barral, Michael Cantara, Julius de Hond, and Yu-Kun Lu, all members of the MIT-Harvard Center for Ultracold Atoms, the Department of Physics, and the Research Laboratory of Electronics at MIT.

The full study was published in the journal Science.

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"Impossible" quantum effects seen when squishing atoms together - Earth.com

Tauonium: The Smallest and Heaviest Atom with Pure Electromagnetic Interaction. Credit: Science China Press

Recent discoveries in quantum physics have revealed simpler atomic structures than hydrogen, involving pure electromagnetic interactions between particles like electrons and their antiparticles. This advancement has significant implications for our understanding of quantum mechanics and fundamental physics, highlighted by new methods for detecting tauonium, which could revolutionize measurements of particle physics.

The hydrogen atom was once considered the simplest atom in nature, composed of a structureless electron and a structured proton. However, as research progressed, scientists discovered a simpler type of atom, consisting of structureless electrons (e-), muons (-), or tauons (-) and their equally structureless antiparticles. These atoms are bound together solely by electromagnetic interactions, with simpler structures than hydrogen atoms, providing a new perspective on scientific problems such as quantum mechanics, fundamental symmetry, and gravity.

To date, only two types of atoms with pure electromagnetic interactions have been discovered: the electron-positron bound state discovered in 1951 (Phys Rev 1951;82:455) and the electron-antimuon bound state discovered in 1960 (Phys Rev Lett 1960;5:63). Over the past 64 years, there have been no other signs of such atoms with pure electromagnetic interactions, although there are some proposals to search for them in cosmic rays or high-energy colliders.

Tauonium, composed of a tauon and its antiparticle, has a Bohr radius of only 30.4 femtometers (1 femtometer = 10-15 meters), approximately 1/1741 (0.057%) of the Bohr radius of a hydrogen atom. This implies that tauonium can test the fundamental principles of quantum mechanics and quantum electrodynamics at smaller scales, providing a powerful tool for exploring the mysteries of the micro material world.

Recently, a study titled Novel method for identifying the heaviest QED atom was published in the comprehensive journal Science Bulletin, proposing a new approach used to discover tauonium. The study demonstrates that by collecting data of 1.5 ab-1 near the threshold of tauon pair production at an electron and positron collider, and selecting signal events containing charged particles accompanied by the undetected neutrinos carrying away energy, the significance of observing tauonium will exceed 5. This indicates a strong experimental evidence for the existence of tauonium.

The study also found that using the same data, the precision of measuring the tau lepton mass can be improved to an unprecedented level of 1 keV, two orders of magnitude higher than the highest precision achieved by current experiments. This achievement will not only contribute to the precise testing of the electroweak theory in the Standard Model but also have profound implications for fundamental physics questions such as lepton flavor universality.

This achievement serves as one of the most important physical objectives of the proposed Super Tau-Charm Facility (STCF) in China or the Super Charm-Tau Factory (SCTF) in Russia: to discover the smallest and heaviest atom with pure electromagnetic interactions by running the machine near the tauon pair threshold for one year and to measure the tau lepton mass with a high precision. These discoveries will provide deeper insights and understanding into humanitys exploration of the microscopic world.

Reference: Novel method for identifying the heaviest QED atom by Jing-Hang Fu, Sen Jia, Xing-Yu Zhou, Yu-Jie Zhang, Cheng-Ping Shen and Chang-Zheng Yuan, 4 April 2024, Science Bulletin. DOI: 10.1016/j.scib.2024.04.003

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Beyond Hydrogen: Discovery of Tiny New Atom Tauonium With Massive Implications - SciTechDaily

Harvard scientists have demonstrated that quantum coherence can persist through chemical reactions in ultracold molecules, suggesting broader applications for quantum information science and potentially in more common environmental conditions.

If you zoom in on a chemical reaction to the quantum level, youll notice that particles behave like waves that can ripple and collide. Scientists have long sought to understand quantum coherence, the ability of particles to maintain phase relationships and exist in multiple states simultaneously; this is akin to all parts of a wave being synchronized. It has been an open question whether quantum coherence can persist through a chemical reaction where bonds dynamically break and form.

Now, for the first time, a team of Harvard scientists has demonstrated the survival of quantum coherence in a chemical reaction involving ultracold molecules. These findings highlight the potential of harnessing chemical reactions for future applications in quantum information science.

I am extremely proud of our work investigating a very fundamental property of a chemical reaction where we really didnt know what the result would be, said senior co-author Kang-Kuen Ni, Theodore William Richards Professor of Chemistry and Professor of Physics. It was really gratifying to do an experiment to find out what Mother Nature tells us.

In the paper, published in Science, the researchers detailed how they studied a specific atom-exchange chemical reaction in an ultra-cold environment involving 40K87Rb bialkali molecules, where two potassium-rubidium (KRb) molecules react to form potassium (K2) and rubidium (Rb2) products. The team prepared the initial nuclear spins in KRb molecules in an entangled state by manipulating magnetic fields and then examined the outcome with specialized tools. In the ultra-cold environment, the Ni Lab was able to track the nuclear spin degrees of freedom and to observe the intricate quantum dynamics underlying the reaction process and outcome.

The work was undertaken by several members of Nis Lab, including Yi-Xiang Liu, Lingbang Zhu, Jeshurun Luke, J.J. Arfor Houwman, Mark C. Babin, and Ming-Guang Hu.

Utilizing laser cooling and magnetic trapping, the team was able to cool their molecules to just a fraction of a degree above Absolute Zero. In this ultracold environment, of just 500 nanoKelvin, molecules slow down, enabling scientists to isolate, manipulate, and detect individual quantum states with remarkable precision. This control facilitates the observation of quantum effects such as superposition, entanglement, and coherence, which play fundamental roles in the behavior of molecules and chemical reactions.

By employing sophisticated techniques, including coincidence detection where the researchers can pick out the exact pairs of reaction products from individual reaction events, the researchers were able to map and describe the reaction products with precision. Previously, they observed the partitioning of energy between the rotational and translational motion of the product molecules to be chaotic [Nature 593, 379-384 (2021)]. Therefore, it is surprising to find quantum order in the form of coherence in the same underlying reaction dynamics, this time in the nuclear spin degree of freedom.

The results revealed that quantum coherence was preserved within the nuclear spin degree of freedom throughout the reaction. The survival of coherence implied that the product molecules, K2 and Rb2, were in an entangled state, inheriting the entanglement from the reactants. Furthermore, by deliberately inducing decoherence in the reactants, the researchers demonstrated control over the reaction product distribution.

Going forward, Ni hopes to rigorously prove that the product molecules were entangled, and she is optimistic that quantum coherence can persist in non-ultracold environments.

We believe the result is general and not necessarily limited to low temperatures and could happen in more warm and wet conditions, Ni said. That means there is a mechanism for chemical reactions that we just didnt know about before.

First co-author and graduate student Lingbang Zhu sees the experiment as an opportunity to expand peoples understanding about chemical reactions in general.

We are probing phenomena that are possibly occurring in nature, Zhu said. We can try to broaden our concept to other chemical reactions. Although the electronic structure of KRb might be different, the idea of interference in reactions could be generalized to other chemical systems as well.

Reference: Quantum interference in atom-exchange reactions by Yi-Xiang Liu, Lingbang Zhu, Jeshurun Luke, J. J. Arfor Houwman, Mark C. Babin, Ming-Guang Hu and Kang-Kuen Ni, 16 May 2024, Science. DOI: 10.1126/science.adl6570

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Quantum Coherence: Harvard Scientists Uncover Hidden Order in Chemical Chaos - SciTechDaily