6,833 research outputs found
Generating multi-atom entangled W states via light-matter interface based fusion mechanism
W state is a key resource in quantum communication. Fusion technology has
been proven to be a good candidate for preparing a large-size W state from two
or more small-size W states in linear optical system. It is of great importance
to study how to fuse W states via light-matter interface. Here we show that it
is possible to prepare large-size W-state networks using a fusion mechanism in
cavity QED system. The detuned interaction between three atoms and a vacuum
cavity mode constitute the main fusion mechanism, based on which two or three
small-size atomic W states can be fused into a larger-size W state. If no
excitation is detected from those three atoms, the remaining atoms are still in
the product of two or three new W states, which can be re-fused. The
complicated Fredkin gate used in the previous fusion schemes is avoided here. W
states of size 2 can be fused as well. The feasibility analysis shows that our
fusion processes maybe implementable with the current technology. Our results
demonstrate how the light-matter interaction based fusion mechanism can be
realized, and may become the starting point for the fusion of multipartite
entanglement in cavity QED system.Comment: 9 pages, 2 figure
Experimentally exploring compressed sensing quantum tomography
In the light of the progress in quantum technologies, the task of verifying
the correct functioning of processes and obtaining accurate tomographic
information about quantum states becomes increasingly important. Compressed
sensing, a machinery derived from the theory of signal processing, has emerged
as a feasible tool to perform robust and significantly more resource-economical
quantum state tomography for intermediate-sized quantum systems. In this work,
we provide a comprehensive analysis of compressed sensing tomography in the
regime in which tomographically complete data is available with reliable
statistics from experimental observations of a multi-mode photonic
architecture. Due to the fact that the data is known with high statistical
significance, we are in a position to systematically explore the quality of
reconstruction depending on the number of employed measurement settings,
randomly selected from the complete set of data, and on different model
assumptions. We present and test a complete prescription to perform efficient
compressed sensing and are able to reliably use notions of model selection and
cross-validation to account for experimental imperfections and finite counting
statistics. Thus, we establish compressed sensing as an effective tool for
quantum state tomography, specifically suited for photonic systems.Comment: 12 pages, 5 figure
Cross-verification of independent quantum devices
Quantum computers are on the brink of surpassing the capabilities of even the
most powerful classical computers. This naturally raises the question of how
one can trust the results of a quantum computer when they cannot be compared to
classical simulation. Here we present a verification technique that exploits
the principles of measurement-based quantum computation to link quantum
circuits of different input size, depth, and structure. Our approach enables
consistency checks of quantum computations within a device, as well as between
independent devices. We showcase our protocol by applying it to five
state-of-the-art quantum processors, based on four distinct physical
architectures: nuclear magnetic resonance, superconducting circuits, trapped
ions, and photonics, with up to 6 qubits and 200 distinct circuits
Interfering trajectories in experimental quantum-enhanced stochastic simulation
Simulations of stochastic processes play an important role in the
quantitative sciences, enabling the characterisation of complex systems. Recent
work has established a quantum advantage in stochastic simulation, leading to
quantum devices that execute a simulation using less memory than possible by
classical means. To realise this advantage it is essential that the memory
register remains coherent, and coherently interacts with the processor,
allowing the simulator to operate over many time steps. Here we report a
multi-time-step experimental simulation of a stochastic process using less
memory than the classical limit. A key feature of the photonic quantum
information processor is that it creates a quantum superposition of all
possible future trajectories that the system can evolve into. This
superposition allows us to introduce, and demonstrate, the idea of comparing
statistical futures of two classical processes via quantum interference. We
demonstrate interference of two 16-dimensional quantum states, representing
statistical futures of our process, with a visibility of 0.96 0.02.Comment: 9 pages, 5 figure
Directionally-unbiased unitary optical devices in discrete-time quantum walks
The optical beam splitter is a widely-used device in photonics-based quantum information processing. Specifically, linear optical networks demand large numbers of beam splitters for unitary matrix realization. This requirement comes from the beam splitter property that a photon cannot go back out of the input ports, which we call “directionally-biased”. Because of this property, higher dimensional information processing tasks suffer from rapid device resource growth when beam splitters are used in a feed-forward manner. Directionally-unbiased linear-optical devices have been introduced recently to eliminate the directional bias, greatly reducing the numbers of required beam splitters when implementing complicated tasks. Analysis of some originally directional optical devices and basic principles of their conversion into directionally-unbiased systems form the base of this paper. Photonic quantum walk implementations are investigated as a main application of the use of directionally-unbiased systems. Several quantum walk procedures executed on graph networks constructed using directionally-unbiased nodes are discussed. A significant savings in hardware and other required resources when compared with traditional directionally-biased beam-splitter-based optical networks is demonstrated.Accepted manuscriptPublished versio
Investigation of critical slowing down in a bistable S-SEED
A simulation of S-SEED switching based upon experimental data is developed that includes the effect of critical slowing down. The simulation's accuracy is demonstrated by close agreement with the results from experimental S-SEED switching. The simulation is subsequently used to understand how the phenomenon of critical slowing down applies to switching of an S-SEED and how the effect on photonic analog-to-digital (A/D) converter performance may be minimized.B. A. Clare, K. A. Corbett, K. J. Grant, P. B. Atanackovic, W. Marwood and J. Munc
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