979 research outputs found
Overarching framework between Gaussian quantum discord and Gaussian quantum illumination
We cast the problem of illuminating an object in a noisy environment into a
communication protocol. A probe is sent into the environment, and the presence
or absence of the object constitutes a signal encoded on the probe. The probe
is then measured to decode the signal. We calculate the Holevo information and
bounds to the accessible information between the encoded and received signal
with two different Gaussian probes---an Einstein-Podolsky-Rosen (EPR) state and
a coherent state. We also evaluate the Gaussian discord consumed during the
encoding process with the EPR probe. We find that the Holevo quantum advantage,
defined as the difference between the Holevo information obtained from the EPR
and coherent state probes, is approximately equal to the discord consumed.
These quantities become exact in the typical illumination regime of low object
reflectivity and low probe energy. Hence we show that discord is the resource
responsible for the quantum advantage in Gaussian quantum illumination.Comment: 12 pages, 8 figure
Explicit capacity-achieving receivers for optical communication and quantum reading
An important practical open question has been to design explicit, structured optical receivers that achieve the Holevo limit in the contexts of optical communication and “quantum reading.” The Holevo limit is an achievable rate that is higher than the Shannon limit of any known optical receiver. We demonstrate how a sequential decoding approach can achieve the Holevo limit for both of these settings. A crucial part of our scheme for both settings is a non-destructive “vacuum-or-not” measurement that projects an n-symbol modulated codeword onto the n-fold vacuum state or its orthogonal complement, such that the post-measurement state is either the n-fold vacuum or has the vacuum removed from the support of the n symbols' joint quantum state. The sequential decoder for optical communication requires the additional ability to perform multimode optical phase-space displacements - realizable using a beamsplitter and a laser, while the sequential decoder for quantum reading also requires the ability to perform phase-shifting (realizable using a phase plate) and online squeezing (a phase-sensitive amplifier)
SU(3) Quantum Interferometry with single-photon input pulses
We develop a framework for solving the action of a three-channel passive
optical interferometer on single-photon pulse inputs to each channel using
SU(3) group-theoretic methods, which can be readily generalized to higher-order
photon-coincidence experiments. We show that features of the coincidence plots
vs relative time delays of photons yield information about permanents,
immanants, and determinants of the interferometer SU(3) matrix
Quantum Illumination with Gaussian States
An optical transmitter irradiates a target region containing a bright
thermal-noise bath in which a low-reflectivity object might be embedded. The
light received from this region is used to decide whether the object is present
or absent. The performance achieved using a coherent-state transmitter is
compared with that of a quantum illumination transmitter, i.e., one that
employs the signal beam obtained from spontaneous parametric downconversion
(SPDC). By making the optimum joint measurement on the light received from the
target region together with the retained SPDC idler beam, the quantum
illumination system realizes a 6 dB advantage in error probability exponent
over the optimum reception coherent-state system. This advantage accrues
despite there being no entanglement between the light collected from the target
region and the retained idler beam.Comment: 4 pages, 1 figur
- …