4,459 research outputs found
Evaluation of routines for numerical solution of the matrix equation AX + XA sup T + B = 0
Evaluation of routines for numerical solution of matrix equation for time-invariant linear system
Scalable boson-sampling with time-bin encoding using a loop-based architecture
We present an architecture for arbitrarily scalable boson-sampling using two
nested fiber loops. The architecture has fixed experimental complexity,
irrespective of the size of the desired interferometer, whose scale is limited
only by fiber and switch loss rates. The architecture employs time-bin
encoding, whereby the incident photons form a pulse train, which enters the
loops. Dynamically controlled loop coupling ratios allow the construction of
the arbitrary linear optics interferometers required for boson-sampling. The
architecture employs only a single point of interference and may thus be easier
to stabilize than other approaches. The scheme has polynomial complexity and
could be realized using demonstrated present-day technologies.Comment: 7 pages, 7 figure
Sampling arbitrary photon-added or photon-subtracted squeezed states is in the same complexity class as boson sampling
Boson sampling is a simple model for non-universal linear optics quantum
computing using far fewer physical resources than universal schemes. An input
state comprising vacuum and single photon states is fed through a Haar-random
linear optics network and sampled at the output using coincidence
photodetection. This problem is strongly believed to be classically hard to
simulate. We show that an analogous procedure implements the same problem,
using photon-added or -subtracted squeezed vacuum states (with arbitrary
squeezing), where sampling at the output is performed via parity measurements.
The equivalence is exact and independent of the squeezing parameter, and hence
provides an entire class of new quantum states of light in the same complexity
class as boson sampling.Comment: 5 pages, 2 figure
Boson sampling with displaced single-photon Fock states versus single-photon-added coherent states---The quantum-classical divide and computational-complexity transitions in linear optics
Boson sampling is a specific quantum computation, which is likely hard to
implement efficiently on a classical computer. The task is to sample the output
photon number distribution of a linear optical interferometric network, which
is fed with single-photon Fock state inputs. A question that has been asked is
if the sampling problems associated with any other input quantum states of
light (other than the Fock states) to a linear optical network and suitable
output detection strategies are also of similar computational complexity as
boson sampling. We consider the states that differ from the Fock states by a
displacement operation, namely the displaced Fock states and the photon-added
coherent states. It is easy to show that the sampling problem associated with
displaced single-photon Fock states and a displaced photon number detection
scheme is in the same complexity class as boson sampling for all values of
displacement. On the other hand, we show that the sampling problem associated
with single-photon-added coherent states and the same displaced photon number
detection scheme demonstrates a computational complexity transition. It
transitions from being just as hard as boson sampling when the input coherent
amplitudes are sufficiently small, to a classically simulatable problem in the
limit of large coherent amplitudes.Comment: 7 pages, 3 figures; published versio
The creation of large photon-number path entanglement conditioned on photodetection
Large photon-number path entanglement is an important resource for enhanced
precision measurements and quantum imaging. We present a general constructive
protocol to create any large photon number path-entangled state based on the
conditional detection of single photons. The influence of imperfect detectors
is considered and an asymptotic scaling law is derived.Comment: 6 pages, 4 figure
Parity Measurement is Sufficient for Phase Estimation at the Quantum Cramer-Rao Bound for Path-Symmetric States
In this letter, we show that for all the so-called path-symmetric states, the
measurement of parity of photon number at the output of an optical
interferometer achieves maximal phase sensitivity at the quantum Cramer-Rao
bound. Such optimal phase sensitivity with parity is attained at a suitable
bias phase, which can be determined a priori. Our scheme is applicable for
local phase estimation
Optical Communication Noise Rejection Using Correlated Photons
This paper describes a completely new way to perform noise rejection using a
two-photon sensitive detector and taking advantage of the properties of
correlated photons to improve an optical communications link in the presence of
uncorrelated noise. In particular, a detailed analysis is made of the case
where a classical link would be saturated by an intense background, such as
when a satellite is in front of the sun,and identifies a regime where the
quantum correlating system has superior performance.Comment: 12 pages, 1 figure, 1 tabl
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