China

Nonlinear optical interaction at a single photon level plays a key role in quantum optical information processing. One of its important applications is optical switching with extremely low power consumption. Although optical switching controlled by a few photons has been demonstrated using strongly coupled quantum dot-photonic crystal cavity systems, the strong coupling regime brings significant fabrication challenges as high cavity quality factor and accurate QD positioning are required. This becomes more problematic for integrated photonic circuits where the cavity Q-factor is strongly degraded due to the waveguide coupling. In this work, we show that low-photon number (~2 photons) optical switching can be realized with a QD weakly coupled to a low-Q (only 600) cavity in the high Purcell factor regime. Our scheme significantly relaxes the fabrication requirement while achieving high switching speed (22.7 ps), high switching contrast (39%), and large tunability. Our work paves the way towards the practical quantum optical switch, especially for on-chip photonic circuits.

Quantum 2020

Ultrafast few-photon switching with a coherently driven quantum dot in the high Purcell factor regime

weak coupling

photonic crystal cavity

single-photon optical switch

quantum dot

The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.


Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. The broad themes covered by Quantum 2020 included:

Quantum communication;
Quantum computing and quantum simulation;
Quantum sensing, metrology and imaging;
Quantum information theory, software and algorithms;
Quantum foundations;
Quantum technology in industry.
The four-day event featured talks from world-renowned scientists, interactive poster sessions and two exciting panel discussions on the themes of Quantum Technology in Industry and Quantum Technology Programmes Around the World.


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The Institute of Physics and IOP Publishing, in partnership with the Chinese Physical Society (CPS) and the University of Science and Technology of China (USTC) are proud to have brought together the international quantum science community online for this inaugural conference.

Early career and leading researchers from universities, industry and government worldwide came together to share, learn and collaborate on the latest research and emerging areas of high interest across quantum science and technology. 

poster

Quantum key distribution (QKD) is one of the most practical applications in quantum information processing, which can generate information-theoretical secure keys between remote parties. With the help of the wavelength-division multiplexing technique, QKD has been integrated with the classical optical communication networks. The wavelength-division multiplexing can be further improved by the mode-wavelength dual multiplexing technique with few-mode fiber (FMF), which has additional modal isolation and large effective core area of mode, and particularly is practical in fabrication and splicing technology compared with the multi-core fiber. Here, we present for the first time a QKD implementation coexisting with classical optical communication over weakly-coupled FMF using all-fiber mode-selective couplers. The co-propagation of QKD with one 100 Gbps classical data channel at -2.60 dBm launched power is achieved over 86 km FMF with 1.3 kbps real-time secure key generation. Compared with single-mode fiber using wavelength-division multiplexing, given the same fiber-input power, the Raman noise in FMF using the mode-wavelength dual multiplexing is reduced by 86% in average. Our work implements an important approach to the integration between QKD and classical optical communication and previews the compatibility of quantum communications with the next-generation mode division multiplexing networks.

Long-distance transmission of quantum key distribution coexisting with classical optical communication over a weakly-coupled few-mode fiber

The prospects of laterally-grown quasi-AlGaN/GaN/AlGaN hetero-structure High-Electron-Mobility-Avalanche-Transit-Time (HEMATT) oscillator as high-power THz-signal source is studied through an indigenously developed Quantum-Drift–Diffusion simulator and experimental verification is reported. Active region of the HEMATT oscillator consists of two-Dimensional Electron Gas (2-DEG), trapped within a GaN quantum well that lies in between AlGaN barriers on either side. Both anode and cathode consist of GaN. Under reverse-biased condition, GaN/AlGaN band offset forces minority electrons to enter into the heterostructure active region and remain confined within the GaN quantum well. Carrier current generation in this 2-DEG active region is due to the quantum confinement of minority electrons rather than conventional tunneling phenomenon. Such quantum confinement is effectively functioning as the gate-control terminal as in conventional HEMTs. Introduction of quasi-AlGaN instead of alloy AlGaN, constitutes of alternate fine layers of AlN/GaN, results in carrier mobility doubling (800cm2/V-sec to 1600cm2/V-sec). A subtle interplay between bound and quasi-bound states is observed due to the quasi-AlGaN barrier. The study reveals a spectacular optical sensitivity with designed HEMATT oscillators. This for the first time opens the prospect of newly reported HEMATT oscillators in quantum sensing to cater the needs of ever growing, sophisticated defense and industrial applications.

A 2-terminal quasi-AlGaN/GaN/AlGaN HEMATT oscillator as quanta-image sensor for single-photon detection applications in defense industry

Entanglement plays a central role in quantum information processing and quantum physics. However, few effective ways are known to detect the amount of entanglement of an unknown quantum state. Here, we propose a scheme to estimate the entanglement negativity for any bipartition of a composite system. The proposed scheme is based on the random unitary evolution and local measurements on a single-copy quantum state, which is more practical compared with former methods based on collective measurements on many copies of the identical state. Meanwhile, we generalize the scheme to quantify the total correlation. We demonstrate the efficiency of the scheme with statistical analyses and numerical simulations. Our scheme is quite suitable for state-of-the-art quantum platforms, which can serve as a useful benchmarking tool to advance quantum technologies and a probe to study fundamental quantum physics like entanglement dynamics.

Single-Copies Estimation of Entanglement Negativity

Quantum antiferromagnet is of fundamental interest as it becomes a fertile ground for studying exotic many-body states including spin liquids and high-temperature superconductors. Compared with condensed matter systems, ultracold gases in optical lattices can be microscopically engineered and provide a unique opportunity for exploring bosonic magnetism and spin dynamics. Here, we report on the creation of a one-dimensional Heisenberg antiferromagnet with ultracold bosons. In a two-component Bose-Hubbard system, we switch the sign of the spin-exchange interaction and realize the isotropic antiferromagnetic Heisenberg model in an extended 70-site chain. Starting from a low-entropy N\'eel-ordered state, the bosonic antiferromagnet is approached via an optimized adiabatic passage. We probe the evolution of staggered magnetization and spin correlations of the system, revealing the coherent establishment of the antiferromagnetism. Furthermore, the characteristic spin-rotational symmetry of the state and its robustness against decoherence are verified. Our experiment demonstrates a novel way for generating many-body spin correlations and exploring exotic forms of magnetism.

Realization of a bosonic antiferromagnet

Continuous variable quantum key distribution (CV-QKD) has made great progress recent years. Throughput of error correction is one of the bottlenecks for CV-QKD. For typical distance of CV-QKD system, the signal-to-noise ratio is low, and a large number of iterations is needed for decoder. Since scheduling strategy is an important factor of the decoder’s convergence rate, in this paper, the performance of three different scheduling strategies (flooding scheduling, layered scheduling by row, layered scheduling by column) is compared. The algorithm complexity, adaptation to the parity check matrix, and throughput performance are studied. For the typical parity check matrix for CV-QKD system, the results show that layered scheduling by column is the best method. Throughput of more than 70 Mbits/s is achieved by this method, which surpasses the record in the literature and can improve the real-time processing capacity of CV-QKD system.

Study on error correction decoder scheduling strategies for continuous variable quantum key distribution system

"HqHop: Hybrid Quantum Hopfield Neural Network for Portfolio Selection

RP Mahajan 
 
Faculty at Dept. of Computer Science & Engineering, SIRT, SAGE University, India
E-mail: rpmahajan.sage@gmail.com ; rpmahajan@yahoo.com

 
Abstract: Classical Hopfield neural networks (CHNN) are known for solving portfolio selection problem for asset management. A Hybrid Quantum Hopfield Neural Network (HqHop) is proposed to solve portfolio selection problem based on Markowitz mean variance approach. Due to the large number of portfolios, the CHNN requires huge memory and processing power. The inbuilt parallelism in CHNN makes it more suitable for quantum based system. This paper details an approach, perhaps the first time, for the solution of portfolio selection problem using the involved concept. The developed HqHop can be used for solving other optimization problems as well.

"

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Long-distance transmission of quantum key distribution coexisting with classical optical communication over a weakly-coupled few-mode fiber

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