More Like this

1. Large-alphabet time-bin quantum key distribution and Einstein–Podolsky–Rosen steering via dispersive optics

   https://doi.org/10.1088/2058-9565/ad0f6f  

   Chang, Kai-Chi ; Sarihan, Murat Can ; Cheng, Xiang ; Zhang, Zheshen ; Wong, Chee Wei ( December 2023 , Quantum Science and Technology)

   Quantum key distribution (QKD) has established itself as a groundbreaking technology, showcasing inherent security features that are fundamentally proven. Qubit-based QKD protocols that rely on binary encoding encounter an inherent constraint related to the secret key capacity. This limitation restricts the maximum secret key capacity to one bit per photon. On the other hand, qudit-based QKD protocols have their advantages in scenarios where photons are scarce and noise is present, as they enable the transmission of more than one secret bit per photon. While proof-of-principle entangled-based qudit QKD systems have been successfully demonstrated over the years, the current limitation lies in the maximum distribution distance, which remains at 20 km fiber distance. Moreover, in these entangled high-dimensional QKD systems, the witness and distribution of quantum steering have not been shown before. Here we present a high-dimensional time-bin QKD protocol based on energy-time entanglement that generates a secure finite-length key capacity of 2.39 bit/coincidences and secure cryptographic finite-length keys at 0.24 Mbits s⁻¹in a 50 km optical fiber link. Our system is built entirely using readily available commercial off-the-shelf components, and secured by nonlocal dispersion cancellation technique against collective Gaussian attacks. Furthermore, we set new records for witnessing both energy-time entanglement and quantum steering over different fiber distances. When operating with a quantum channel loss of 39 dB, our system retains its inherent characteristic of utilizing large-alphabet. This enables us to achieve a secure key rate of 0.30 kbits s⁻¹and a secure key capacity of 1.10 bit/coincidences, considering finite-key effects. Our experimental results closely match the theoretical upper bound limit of secure cryptographic keys in high-dimensional time-bin QKD protocols (Moweret al2013Phys. Rev.A87062322; Zhanget al2014Phys. Rev. Lett.112120506), and outperform recent state-of-the-art qubit-based QKD protocols in terms of secure key throughput using commercial single-photon detectors (Wengerowskyet al2019Proc. Natl Acad. Sci.1166684; Wengerowskyet al2020npj Quantum Inf.65; Zhanget al2014Phys. Rev. Lett.112120506; Zhanget al2019Nat. Photon.13839; Liuet al2019Phys. Rev. Lett.122160501; Zhanget al2020Phys. Rev. Lett.125010502; Weiet al2020Phys. Rev.X10031030). The simple and robust entanglement-based high-dimensional time-bin protocol presented here provides potential for practical long-distance quantum steering and QKD with multiple secure bits-per-coincidence, and higher secure cryptographic keys compared to mature qubit-based QKD protocols.

    

   more » « less
2. Imaging topology of Hofstadter ribbons

   https://doi.org/10.1088/1367-2630/ab165b  

   Genkina, Dina ; Aycock, Lauren M. ; Lu, Hsin-I ; Lu, Mingwu ; Pineiro, Alina M. ; Spielman, I. B. ( May 2019 , New Journal of Physics)

   Physical systems with non-trivial topological order find direct applications in metrology (Klitzinget al1980Phys.Rev. Lett.45494–7) and promise future applications in quantum computing (Freedman 2001Found. Comput. Math.1183–204; Kitaev 2003Ann. Phys.3032–30). The quantum Hall effect derives from transverse conductance, quantized to unprecedented precision in accordance with the system’s topology (Laughlin 1981Phys. Rev.B235632–33). At magnetic fields beyond the reach of current condensed matter experiment, around${\mathrm{10}}^{\mathrm{4}}$T, this conductance remains precisely quantized with values based on the topological order (Thoulesset al1982Phys. Rev. Lett.49405–8). Hitherto, quantized conductance has only been measured in extended 2D systems. Here, we experimentally studied narrow 2D ribbons, just 3 or 5 sites wide along one direction, using ultracold neutral atoms where such large magnetic fields can be engineered (Jaksch and Zoller 2003New J. Phys.556; Miyakeet al2013Phys. Rev. Lett.111185302; Aidelsburgeret al2013Phys. Rev. Lett.111185301; Celiet al2014Phys. Rev. Lett.112043001; Stuhlet al2015Science3491514; Manciniet al2015Science3491510; Anet al2017Sci. Adv.3). We microscopically imaged the transverse spatial motion underlying the quantized Hall effect. Our measurements identify the topological Chern numbers with typical uncertainty of$\mathrm{5}\%$, and show that although band topology is only properly defined in infinite systems, its signatures are striking even in nearly vanishingly thin systems.

    

   more » « less
3. Microscopic reversibility and emergent elasticity in ultrastable granular systems

   https://doi.org/10.3389/fphy.2022.1048683  

   Zhao, Yiqiu ; Zhao, Yuchen ; Wang, Dong ; Zheng, Hu ; Chakraborty, Bulbul ; Socolar, Joshua E. ( November 2022 , Frontiers in Physics)

   In a recent paper (Zhao et al., Phys Rev X, 2022, 12: 031,021), we reported experimental observations of “ultrastable” states in a shear-jammed granular system subjected to small-amplitude cyclic shear. In such states, all the particle positions and contact forces are reproduced after each shear cycle so that a strobed image of the stresses and particle positions appears static. In the present work, we report further analyses of data from those experiments to characterize both global and local responses of ultrastable states within a shear cycle, not just the strobed dynamics. We find that ultrastable states follow a power-law relation between shear modulus and pressure with an exponentβ≈ 0.5, reminiscent of critical scaling laws near jamming. We also examine the evolution of contact forces measured using photoelasticimetry. We find that there are two types of contacts: non-persistent contacts that reversibly open and close; and persistent contacts that never open and display no measurable sliding. We show that the non-persistent contacts make a non-negligible contribution to the emergent shear modulus. We also analyze the spatial correlations of the stress tensor and compare them to the predictions of a recent theory of the emergent elasticity of granular solids, the Vector Charge Theory of Granular mechanics and dynamics (VCTG) (Nampoothiri et al., Phys Rev Lett, 2020, 125: 118,002). We show that our experimental results can be fit well by VCTG, assuming uniaxial symmetry of the contact networks. The fits reveal that the response of the ultrastable states to additional applied stress is substantially more isotropic than that of the original shear-jammed states. Our results provide important insight into the mechanical properties of frictional granular solids created by shear.

    

   more » « less
4. Three-dimensional simulations of undulatory and amoeboid swimmers in viscoelastic fluids

   https://doi.org/10.1039/C8SM02518E  

   Binagia, Jeremy P. ; Guido, Christopher J. ; Shaqfeh, Eric S. ( June 2019 , Soft Matter)

   Microorganisms often move through viscoelastic environments, as biological fluids frequently have a rich microstructure owing to the presence of large polymeric molecules. Research on the effect of fluid elasticity on the swimming kinematics of these organisms has usually been focused on those that move via cilia or flagellum. Experimentally, Shen (X. N. Shen et al. , Phys. Rev. Lett. , 2011, 106 , 208101) reported that the nematode C. elegans , a model organism used to study undulatory motion, swims more slowly as the Deborah number describing the fluid's elasticity is increased. This phenomenon has not been thoroughly studied via a fully resolved three-dimensional simulation; moreover, the effect of fluid elasticity on the swimming speed of organisms moving via euglenoid movement, such as E. gracilis , is completely unknown. In this study, we discuss the simulation of the arbitrary motion of an undulating or pulsating swimmer that occupies finite volume in three dimensions, with the ability to specify any differential viscoelastic rheological model for the surrounding fluid. To accomplish this task, we use a modified version of the Immersed Finite Element Method presented in a previous paper by Guido and Saadat in 2018 (A. Saadat et al. , Phys. Rev. E , 2018, 98 , 063316). In particular, this version allows for the simulation of deformable swimmers such that they evolve through an arbitrary set of specified shapes via a conformation-driven force. From our analysis, we observe several key trends not found in previous two-dimensional simulations or theoretical analyses for C. elegans , as well as novel results for the amoeboid motion. In particular, we find that regions of high polymer stress concentrated at the head and tail of the swimming C. elegans are created by strong extensional flow fields and are associated with a decrease in swimming speed for a given swimming stroke. In contrast, in two dimensions these regions of stress are commonly found distributed along the entire body, likely owing to the lack of a third dimension for polymer relaxation. A comparison of swim speeds shows that the calculations in two-dimensional simulations result in an over-prediction of the speed reduction. We believe that our simulation tool accurately captures the swimming motion of the two aforementioned model swimmers and furthermore, allows for the simulation of multiple deformable swimmers, as well as more complex swimming geometries. This methodology opens many new possibilities for future studies of swimmers in viscoelastic fluids. 

   more » « less
5. Single-shot visualization of the optical Kerr effect, ionization, and rotational Raman effect during laser matter interactions via frequency-domain holography

   Dempsey, Dennis ; Nagar, Garima ; Agnes, Jack ; Berger, Russell ; Shim, Bonggu ( June 2021 , APS Division of Atomic, Molecular and Optical Physics Meeting 2021)

   We visualize the ultrafast dynamics caused by intense femtosecond laser pulses in both thin flexible glass as well as gaseous atoms and molecules using single-shot Frequency Domain Holography (FDH) [1-3]. FDH is a robust, single-shot, time-resolved visualization technique that employs chirped pulses. Femtosecond laser micromachining of glass materials relies critically on the Kerr effect and ionization, thus direct observation of their dynamics can help produce optical devices such as waveguides. For gases, single-shot visualization of laser-matter interactions will allow for a better understanding of nonlinear optical phenomena such as filamentation [4] and Raman-induced extreme spectral broadening [5]. Using FDH, we have previously observed the ionization dynamics of thin, flexible glass and measured its nonlinear index [3], and are currently investigating the ultrafast dynamics of gases under intense laser fields. [1] S. P. Le Blanc et al., Opt. Lett. 56, 764-766 (2000). [2] K. Y. Kim et al., APL, 88 4124-4126 (2002). [3] S. Huang et. al., OFC 1-3 (2014). [4] A. Couairon et al., Phys. Rep. 441, 47 (2007). [5] D. Dempsey et al. Opt. Lett. 45, 1252-1255 (2020). 

   more » « less