750 research outputs found
Fundamental limits of quantum-secure covert optical sensing
We present a square root law for active sensing of phase of a single
pixel using optical probes that pass through a single-mode lossy thermal-noise
bosonic channel. Specifically, we show that, when the sensor uses an -mode
covert optical probe, the mean squared error (MSE) of the resulting estimator
scales as ; improving the
scaling necessarily leads to detection by the adversary with high probability.
We fully characterize this limit and show that it is achievable using laser
light illumination and a heterodyne receiver, even when the adversary captures
every photon that does not return to the sensor and performs arbitrarily
complex measurement as permitted by the laws of quantum mechanics.Comment: 13 pages, 1 figure, submitted to ISIT 201
Bounding the quantum limits of precision for phase estimation with loss and thermal noise
We consider the problem of estimating an unknown but constant carrier phase
modulation using a general -- possibly entangled -- -mode optical
probe through independent and identical uses of a lossy bosonic channel
with additive thermal noise. We find an upper bound to the quantum Fisher
information (QFI) of estimating as a function of , the mean and
variance of the total number of photons in the -mode probe, the
transmissivity and mean thermal photon number per mode of the bosonic channel. Since the inverse of QFI provides a lower bound to
the mean-squared error (MSE) of an unbiased estimator of
, our upper bound to the QFI provides a lower bound to the MSE. It
already has found use in proving fundamental limits of covert sensing, and
could find other applications requiring bounding the fundamental limits of
sensing an unknown parameter embedded in a correlated field.Comment: No major changes to previous version. Change in the title and
abstract, change in the presentation and structure, an example of the bound
is now included, and some references were added. Comments are welcom
Covert Communication over Classical-Quantum Channels
The square root law (SRL) is the fundamental limit of covert communication
over classical memoryless channels (with a classical adversary) and quantum
lossy-noisy bosonic channels (with a quantum-powerful adversary). The SRL
states that covert bits, but no more, can be reliably
transmitted in channel uses with bits of secret
pre-shared between the communicating parties. Here we investigate covert
communication over general memoryless classical-quantum (cq) channels with
fixed finite-size input alphabets, and show that the SRL governs covert
communications in typical scenarios. %This demonstrates that the SRL is
achievable over any quantum communications channel using a product-state
transmission strategy, where the transmitted symbols in every channel use are
drawn from a fixed finite-size alphabet. We characterize the optimal constants
in front of for the reliably communicated covert bits, as well as
for the number of the pre-shared secret bits consumed. We assume a
quantum-powerful adversary that can perform an arbitrary joint (entangling)
measurement on all channel uses. However, we analyze the legitimate
receiver that is able to employ a joint measurement as well as one that is
restricted to performing a sequence of measurements on each of channel uses
(product measurement). We also evaluate the scenarios where covert
communication is not governed by the SRL
Covert sensing using floodlight illumination
We propose a scheme for covert active sensing using floodlight illumination
from a THz-bandwidth amplified spontaneous emission (ASE) source and heterodyne
detection. We evaluate the quantum-estimation-theoretic performance limit of
covert sensing, wherein a transmitter's attempt to sense a target phase is kept
undetectable to a quantum-equipped passive adversary, by hiding the signal
photons under the thermal noise floor. Despite the quantum state of each mode
of the ASE source being mixed (thermal), and hence inferior compared to the
pure coherent state of a laser mode, the thousand-times higher optical
bandwidth of the ASE source results in achieving a substantially superior
performance compared to a narrowband laser source by allowing the probe light
to be spread over many more orthogonal temporal modes within a given
integration time. Even though our analysis is restricted to single-mode phase
sensing, this system could be applicable extendible for various practical
optical sensing applications.Comment: We present new results and discuss some results found in
arXiv:1701.06206. Comments are welcom
We Clerked for Justices Scalia and Stevens. America Is Getting Heller Wrong.
In the summer of 2008, the Supreme Court decided District of Columbia v. Heller, in which the court held for the first time that the Second Amendment protected an individual right to gun ownership. We were law clerks to Justice Antonin Scalia, who wrote the majority opinion, and Justice John Paul Stevens, who wrote the lead dissent
Performance of Quantum Preprocessing under Phase Noise
Optical fiber transmission systems form the backbone of today's communication
networks and will be of high importance for future networks as well. Among the
prominent noise effects in optical fiber is phase noise, which is induced by
the Kerr effect. This effect limits the data transmission capacity of these
networks and incurs high processing load on the receiver. At the same time,
quantum information processing techniques offer more efficient solutions but
are believed to be inefficient in terms of size, power consumption and
resistance to noise. Here we investigate the concept of an all-optical joint
detection receiver. We show how it contributes to enabling higher baud-rates
for optical transmission systems when used as a pre-processor, even under high
levels of noise induced by the Kerr effect.Comment: 6 pages, 3 figures; To be published in IEEE GLOBECOM 2022, see this
https://globecom2022.ieee-globecom.or
- …