32 research outputs found
Phase sensitivity at the Heisenberg limit in an SU(1,1) interferometer via parity detection
We theoretically investigate the phase sensitivity with parity detection on
an SU(1,1) interferometer with a coherent state combined with a squeezed vacuum
state. This interferometer is formed with two parametric amplifiers for beam
splitting and recombination instead of beam splitters. We show that the
sensitivity of estimation phase approaches Heisenberg limit and give the
corresponding optimal condition. Moreover, we derive the quantum Cram\'er-Rao
bound of the SU(1,1) interferometer.Comment: 9 pages, 2 figures, 3 table
Inefficiency of classically simulating linear optical quantum computing with Fock-state inputs
Aaronson and Arkhipov recently used computational complexity theory to argue
that classical computers very likely cannot efficiently simulate linear,
multimode, quantum-optical interferometers with arbitrary Fock-state inputs
[Aaronson and Arkhipov, Theory Comput. 9, 143 (2013)]. Here we present an
elementary argument that utilizes only techniques from quantum optics. We
explicitly construct the Hilbert space for such an interferometer and show that
its dimension scales exponentially with all the physical resources. We also
show in a simple example just how the Schr\"odinger and Heisenberg pictures of
quantum theory, while mathematically equivalent, are not in general
computationally equivalent. Finally, we conclude our argument by comparing the
symmetry requirements of multiparticle bosonic to fermionic interferometers
and, using simple physical reasoning, connect the nonsimulatability of the
bosonic device to the complexity of computing the permanent of a large matrix.Comment: 7 pages, 1 figure Published in PRA Phys. Rev. A 89, 022328 (2014
Quantum random walks with multiphoton interference and high-order correlation functions
We show a simulation of quantum random walks (QRWs) with multiple photons using a staggered array of 50/50 beam splitters with a bank of detectors at any desired level. We discuss the multiphoton interference effects that are inherent to this setup, and introduce one, two, and threefold coincidence detection schemes. Feynman diagrams are used to intuitively explain the unique multiphoton interference effects of these QRWs. © 2013 Optical Society of America
Interferometry with Photon-Subtracted Thermal Light
We propose and implement a quantum procedure for enhancing the sensitivity
with which one can determine the phase shift experienced by a weak light beam
possessing thermal statistics in passing through an interferometer. Our
procedure entails subtracting exactly one (which can be generalized to m)
photons from the light field exiting an interferometer containing a
phase-shifting element in one of its arms. As a consequence of the process of
photon subtraction, and somewhat surprisingly, the mean photon number and
signal-to-noise ratio of the resulting light field are thereby increased,
leading to enhanced interferometry. This method can be used to increase
measurement sensitivity in a variety of practical applications, including that
of forming the image of an object illuminated only by weak thermal light