296 research outputs found
Simulability of Imperfect Gaussian and Superposition Boson Sampling
We study the hardness of classically simulating Gaussian boson sampling at
nonzero photon distinguishability. We find that similar to regular boson
sampling, distinguishability causes exponential attenuation of the many-photon
interference terms in Gaussian boson sampling. Barring an open problem in the
theory of matrix permanents, this leads to an efficient classical algorithm to
simulate Gaussian boson sampling in the presence of distinguishability. We also
study a new form of boson sampling based on photon number superposition states,
for which we also show noise sensivity. The fact that such superposition boson
sampling is not simulable with out method at zero distinguishability is the
first evidence for the computational hardness of this problem
Marginal probabilities in boson samplers with arbitrary input states
With the recent claim of a quantum advantage demonstration in photonics by
Zhong et al, the question of the computation of lower-order approximations of
boson sampling with arbitrary quantum states at arbitrary distinguishability
has come to the fore. In this work, we present results in this direction,
building on the results of Clifford and Clifford. In particular, we show:
1) How to compute marginal detection probabilities (i.e. probabilities of the
detection of some but not all photons) for arbitrary quantum states.
2) Using the first result, how to generalize the sampling algorithm of
Clifford and Clifford to arbitrary photon distinguishabilities and arbitrary
input quantum states.
3) How to incorporate truncations of the quantum interference into a sampling
algorithm.
4) A remark considering maximum likelihood verification of the recent
photonic quantum advantage experiment
Benchmarking of Gaussian boson sampling using two-point correlators
Gaussian boson sampling is a promising scheme for demonstrating a quantum
computational advantage using photonic states that are accessible in a
laboratory and, thus, offer scalable sources of quantum light. In this
contribution, we study two-point photon-number correlation functions to gain
insight into the interference of Gaussian states in optical networks. We
investigate the characteristic features of statistical signatures which enable
us to distinguish classical from quantum interference. In contrast to the
typical implementation of boson sampling, we find additional contributions to
the correlators under study which stem from the phase dependence of Gaussian
states and which are not observable when Fock states interfere. Using the first
three moments, we formulate the tools required to experimentally observe
signatures of quantum interference of Gaussian states using two outputs only.
By considering the current architectural limitations in realistic experiments,
we further show that a statistically significant discrimination between quantum
and classical interference is possible even in the presence of loss, noise, and
a finite photon-number resolution. Therefore, we formulate and apply a
theoretical framework to benchmark the quantum features of Gaussian boson
sampling under realistic conditions
Quantum noise limited and entanglement-assisted magnetometry
We study experimentally the fundamental limits of sensitivity of an atomic
radio-frequency magnetometer. First we apply an optimal sequence of state
preparation, evolution, and the back-action evading measurement to achieve a
nearly projection noise limited sensitivity. We furthermore experimentally
demonstrate that Einstein-Podolsky-Rosen (EPR) entanglement of atoms generated
by a measurement enhances the sensitivity to pulsed magnetic fields. We
demonstrate this quantum limited sensing in a magnetometer utilizing a truly
macroscopic ensemble of 1.5*10^12 atoms which allows us to achieve
sub-femtoTesla/sqrt(Hz) sensitivity.Comment: To appear in Physical Review Letters, April 9 issue (provisionally
Simulating boson sampling in lossy architectures
Photon losses are among the strongest imperfections affecting multi-photon
interference. Despite their importance, little is known about their effect on
boson sampling experiments. In this work we show that using classical
computers, one can efficiently simulate multi-photon interference in all
architectures that suffer from an exponential decay of the transmission with
the depth of the circuit, such as integrated photonic circuits or optical
fibers. We prove that either the depth of the circuit is large enough that it
can be simulated by thermal noise with an algorithm running in polynomial time,
or it is shallow enough that a tensor network simulation runs in
quasi-polynomial time. This result suggests that in order to implement a
quantum advantage experiment with single-photons and linear optics new
experimental platforms may be needed
Gaussian Optical Ising Machines
It has recently been shown that optical parametric oscillator (OPO) Ising
machines, consisting of coupled optical pulses circulating in a cavity with
parametric gain, can be used to probabilistically find low-energy states of
Ising spin systems. In this work, we study optical Ising machines that operate
under simplified Gaussian dynamics. We show that these dynamics are sufficient
for reaching probabilities of success comparable to previous work. Based on
this result, we propose modified optical Ising machines with simpler designs
that do not use parametric gain yet achieve similar performance, thus
suggesting a route to building much larger systems.Comment: 6 page
Tensor network states in time-bin quantum optics
The current shift in the quantum optics community towards large-size
experiments -- with many modes and photons -- necessitates new classical
simulation techniques that go beyond the usual phase space formulation of
quantum mechanics. To address this pressing demand we formulate linear quantum
optics in the language of tensor network states. As a toy model, we extensively
analyze the quantum and classical correlations of time-bin interference in a
single fiber loop. We then generalize our results to more complex time-bin
quantum setups and identify different classes of architectures for
high-complexity and low-overhead boson sampling experiments
Boson Sampling in Low-depth Optical Systems
Optical losses are the main obstacle to demonstrating a quantum advantage via
boson sampling without leaving open the possibility of classical spoofing. We
propose a method for generating low-depth optical circuits suitable for boson
sampling with very high efficiencies. Our circuits require only a constant
number of optical components (namely three) to implement an optical
transformation suitable for demonstrating a quantum advantage. Consequently,
our proposal has a constant optical loss regardless of the number of optical
modes. We argue that sampling from our family of circuits is computationally
hard by providing numerical evidence that our family of circuits converges to
that of the original boson sampling proposal in the limit of large optical
systems. Our work opens a new route to demonstrate an optical quantum
advantage.Comment: 11 pages, 6 figure
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