64 research outputs found
On-chip III-V monolithic integration of heralded single photon sources and beamsplitters
We demonstrate a monolithic III-V photonic circuit combining a heralded
single photon source with a beamsplitter, at room temperature and telecom
wavelength. Pulsed parametric down-conversion in an AlGaAs waveguide generates
counterpropagating photons, one of which is used to herald the injection of its
twin into the beamsplitter. We use this configuration to implement an
integrated Hanbury-Brown and Twiss experiment, yielding a heralded second-order
correlation that confirms single-photon
operation. The demonstrated generation and manipulation of quantum states on a
single III-V semiconductor chip opens promising avenues towards real-world
applications in quantum information
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
Joint estimation of phase and phase diffusion for quantum metrology
Phase estimation, at the heart of many quantum metrology and communication
schemes, can be strongly affected by noise, whose amplitude may not be known,
or might be subject to drift. Here, we investigate the joint estimation of a
phase shift and the amplitude of phase diffusion, at the quantum limit. For
several relevant instances, this multiparameter estimation problem can be
effectively reshaped as a two-dimensional Hilbert space model, encompassing the
description of an interferometer phase probed with relevant quantum states --
split single-photons, coherent states or N00N states. For these cases, we
obtain a trade-off bound on the statistical variances for the joint estimation
of phase and phase diffusion, as well as optimum measurement schemes. We use
this bound to quantify the effectiveness of an actual experimental setup for
joint parameter estimation for polarimetry. We conclude by discussing the form
of the trade-off relations for more general states and measurements.Comment: Published in Nature Communications. Supplementary Information
available at
http://www.nature.com/ncomms/2014/140404/ncomms4532/extref/ncomms4532-s1.pd
Interfacing GHz-bandwidth heralded single photons with a room-temperature Raman quantum memory
Photonics is a promising platform for quantum technologies. However, photon
sources and two-photon gates currently only operate probabilistically.
Large-scale photonic processing will therefore be impossible without a
multiplexing strategy to actively select successful events. High
time-bandwidth-product quantum memories - devices that store and retrieve
single photons on-demand - provide an efficient remedy via active
synchronisation. Here we interface a GHz-bandwidth heralded single-photon
source and a room-temperature Raman memory with a time-bandwidth product
exceeding 1000. We store heralded single photons and observe a clear influence
of the input photon statistics on the retrieved light, which agrees with our
theoretical model. The preservation of the stored field's statistics is limited
by four-wave-mixing noise, which we identify as the key remaining challenge in
the development of practical memories for scalable photonic information
processing
Quantum interference enables constant-time quantum information processing
Science, medicine and engineering demand efficient information processing. It is a long-standing goal to use quantum mechanics to significantly improve such computations. The processing routinely involves examining data as a function of complementary variables, e.g., time and frequency. This is done by the Fourier transform approximations which accurately compute inputs of samples in steps. In the quantum domain, an analogous process exists, namely a Fourier transform of quantum amplitudes, which requires exponentially fewer quantum gates. Here, we report a quantum fractional Kravchuk-Fourier transform, a related process suited to finite string processing. Unlike previous demonstrations, our architecture involves only one gate, resulting in constant-time processing of quantum information. The gate exploits a generalized Hong--Ou--Mandel effect, the basis for quantum-photonic information applications. We perform a proof-of-concept experiment by creation of large photon number states, interfering them on a beam splitter and using photon-counting detection. Existing quantum technologies may scale it up towards diverse applications
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