nshu Li

Optimal architectures for long distance quantum communication.

Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (≥1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). Here we present the first systematic comparison of three generations of quantum repeaters by evaluating the cost of both temporal and physical resources, and identify the optimized quantum repeater architecture for a given set of experimental parameters for use in quantum key distribution. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances.Sreraman Muralidharan1∗, Linshu Li2∗, Jungsang Kim, Norbert Lütkenhaus, Mikhail D. Lukin, and Liang Jiang Department of Electrical Engineering, Yale University, New Haven, CT 06511 USA Department of Applied Physics, Yale University, New Haven, CT 06511 USA Department of Electrical and Computer Engineering, Duke University, Durham, NC 27708 USA Institute of Quantum computing, University of Waterloo, N2L 3G1 Waterloo, Canada and Department of Physics, Harvard University, Cambridge, MA 02138, USA∗ (Dated: September 29, 2015)

Cat codes with optimal decoherence suppression for a lossy bosonic channel

We investigate cat codes that can correct multiple excitation losses and identify two types of logical errors: bit-flip errors due to excessive excitation loss and dephasing errors due to quantum backaction from the environment. We show that selected choices of logical subspace and coherent amplitude significantly reduce dephasing errors. The trade-off between the two major errors enables optimized performance of cat codes in terms of minimized decoherence. With high coupling efficiency, we show that one-way quantum repeaters with cat codes feature a boosted secure communication rate per mode when compared to conventional encoding schemes, showcasing the promising potential of quantum information processing with continuous variable quantum codes.

Overcoming erasure errors with multilevel systems

We investigate the usage of highly efficient error correcting codes of multilevel systems to protect encoded quantum information from erasure errors and implementation to repetitively correct these errors. Our scheme makes use of quantum polynomial codes to encode quantum information and generalizes teleportation based error correction for multilevel systems to correct photon losses and operation errors in a fault-tolerant manner. We discuss the application of quantum polynomial codes to one-way quantum repeaters. For various types of operation errors, we identify different parameter regions where quantum polynomial codes can achieve a superior performance compared to qubit based quantum parity codes.

Optimized architectures for long distance quantum communication

Efficient long distance quantum communication with quantum repeaters is discussed. We show that quantum repeater protocols can be classified into three generations, each performs optimally in different parameter regimes. The application of cat codes as a single-mode encoding to one-way quantum repeaters is analyzed.