25,197 research outputs found
Large-Alphabet Encoding Schemes for Floodlight Quantum Key Distribution
Floodlight quantum key distribution (FL-QKD) uses binary phase-shift keying
(BPSK) of multiple optical modes to achieve Gbps secret-key rates (SKRs) at
metropolitan-area distances. We show that FL-QKD's SKR can be doubled by using
32-ary PSK.Comment: 2 pages, 2 figure
Entanglement-Enhanced Lidars for Simultaneous Range and Velocity Measurements
Lidar is a well known optical technology for measuring a target's 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 when 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 and and converts it to a signal-idler photon
pair whose frequencies are and .
Insight into how this transformation provides its benefits is provided through
an analogy to superdense coding.Comment: 7 pages, 3 figure
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