Quntao Zhuang

Optimum mixed-state discrimination for noisy entanglement-enhanced sensing

We propose a structured receiver for optimum mixed-state discrimination in quantum illumination target detection, paving the way for entanglement-enhanced minimum-error-probability sensing in an entanglement-breaking environment.

Floodlight quantum key distribution: A practical route to gigabit-per-second secret-key rates

The channel loss incurred in long-distance transmission places a significant burden on quantum key distribution (QKD) systems: they must defeat a passive eavesdropper who detects all the light lost in the quantum channel and does so without disturbing the light that reaches the intended destination. The current QKD implementation with the highest long-distance secret-key rate meets this challenge by transmitting no more than one photon per bit [Opt. Express 21, 24550-24565 (2013)]. As a result, it cannot achieve the Gbps secret-key rate needed for one-time pad encryption of large data files unless an impractically large amount of multiplexing is employed. We introduce floodlight QKD (FL-QKD), which floods the quantum channel with a high number of photons per bit distributed over a much greater number of optical modes. FL-QKD offers security against the optimum frequency-domain collective attack by transmitting less than one photon per mode and using photon-coincidence channel monitoring, and it is completely immune to passive eavesdropping. More importantly, FL-QKD is capable of a 2 Gbps secret-key rate over a 50 km fiber link, without any multiplexing, using available equipment, i.e., no new technology need be developed. FL-QKD achieves this extraordinary secret-key rate by virtue of its unprecedented secret-key efficiency, in bits per channel use, which exceeds those of state-of-the-art systems by two orders of magnitude.

Floodlight quantum key distribution: Demonstrating a framework for high-rate secure communication

Floodlight quantum key distribution (FL-QKD) is a radically different QKD paradigm that can achieve Gbit/s secret-key rates over metropolitan area distances without multiplexing [Phys. Rev. A 94, 012322 (2016)]. It is a two-way protocol that transmits many photons per bit duration and employs a high-gain optical amplifier, neither of which can be utilized by existing QKD protocols to mitigate channel loss. FL-QKD uses an optical bandwidth that is substantially larger than the modulation rate and performs decoding with a unique broadband homodyne receiver. Essential to FL-QKD is Alices injection of photons from a photon-pair source--in addition to the light used for key generation--into the light she sends to Bob. This injection enables Alice and Bob to quantify Eves intrusion and thus secure FL-QKD against collective attacks. Our proof-of-concept experiment included 10 dB propagation loss--equivalent to 50 km of low-loss fiber--and achieved a 55 Mbit/s secret-key rate (SKR) for a 100 Mbit/s modulation rate, as compared to the state-of-the-art systems 1 Mbit/s SKR for a 1 Gbit/s modulation rate [Opt. Express 21, 24550-24565 (2013)], representing ~500-fold and ~50-fold improvements in secret-key efficiency (SKE) (bits per channel use) and SKR (bits per second), respectively.

Entanglement-enhanced lidars for simultaneous range and velocity measurements

Lidar is a well known optical technology for measuring a targets range and radial velocity. We describe two lidar systems that use entanglement between transmitted signals and retained idlers to obtain significant quantum enhancements in simultaneous measurement of these parameters. The first entanglement-enhanced lidar circumvents the Arthurs-Kelly uncertainty relation for simultaneous measurement of range and radial velocity from detection of a single photon returned from the target. This performance presumes there is no extraneous (background) light, but is robust to the roundtrip loss incurred by the signal photons. The second entanglement-enhanced lidar---which requires a lossless, noiseless environment---realizes Heisenberg-limited accuracies for both its range and radial-velocity measurements, i.e., their root-mean-square estimation errors are both proportional to

Quantum illumination for enhanced detection of Rayleigh-fading targets

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Superadditivity of the Classical Capacity with Limited Entanglement Assistance

when

Entanglement-enhanced Neyman–Pearson target detection using quantum illumination

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Experimental Quantum Key Distribution at 1.3 Gbit/s Secret-Key Rate over a 10-dB-Loss Channel

signal photons are transmitted. These two lidars derive their entanglement-based enhancements from use of a unitary transformation that takes a signal-idler photon pair with frequencies

Additive Classical Capacity of Quantum Channels Assisted by Noisy Entanglement

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Experimental quantum key distribution at 1.3 gigabit-per-second secret-key rate over a 10 dB loss channel

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