1,774 research outputs found
An efficient quantum filter for multiphoton states
We propose a scheme for implementing a multipartite quantum filter that uses
entangled photons as a resource. It is shown that the success probability for
the 2-photon parity filter can be as high as 1/2, which is the highest that has
so far been predicted without the help of universal two-qubit quantum gates.
Furthermore, the required number of ancilla photons is the least of all current
parity filter proposals. Remarkably, the quantum filter operates with
probability 1/2 even in the N-photon case, irregardless of the number of
photons in the input state.Comment: 8 pages, 2 figures, revised version, accepted for publication in J.
Mod. Op
Quantum Information Processing with Single Photons
Photons are natural carriers of quantum information due to their ease of
distribution and long lifetime. This thesis concerns various related aspects of
quantum information processing with single photons. Firstly, we demonstrate
N-photon entanglement generation through a generalised N X N symmetric beam
splitter known as the Bell multiport. A wide variety of 4-photon entangled
states as well as the N-photon W-state can be generated with an unexpected
non-monotonic decreasing probability of success with N. We also show how the
same setup can be used to generate multiatom entanglement. A further study of
multiports also leads us to a multiparticle generalisation of the
Hong-Ou-Mandel dip which holds for all Bell multiports of even number of input
ports. Next, we demonstrate a generalised linear optics based photon filter
that has a constant success probability regardless of the number of photons
involved. This filter has the highest reported success probability and is
interferometrically robust. Finally, we demonstrate how repeat-until-success
quantum computing can be performed with two distant nodes with unit success
probability using only linear optics resource. We further show that using
non-identical photon sources, robustness can still be achieved, an illustration
of the nature and advantages of measurement-based quantum computation. A direct
application to the same setup leads naturally to arbitrary multiphoton state
generation on demand. Finally, we demonstrate how polarisation entanglement of
photons can be detected from the emission of two atoms in a Young's double-slit
type experiment without linear optics, resulting in both atoms being also
maximally entangled.Comment: PhD Thesis, 131 page
Repeat-Until-Success Quantum Computing
We demonstrate the possibility to perform distributed quantum computing using
only single photon sources (atom-cavity-like systems), linear optics and photon
detectors. The qubits are encoded in stable ground states of the sources. To
implement a universal two-qubit gate, two photons should be generated
simultaneously and pass through a linear optics network, where a measurement is
performed on them. Gate operations can be repeated until a success is heralded
without destroying the qubits at any stage of the operation. In contrast to
other schemes, this does not require explicit qubit-qubit interactions, a
priori entangled ancillas nor the feeding of photons into photon sources.Comment: 5 pages, 2 figures, v3: substantially revised, v4: typos correcte
Multi-photon entanglement from distant single photon sources on demand
We describe a scheme that allows for the generation of any desired N-photon
state on demand. Under ideal conditions, this requires only N single photon
sources, laser pulses and linear optics elements. First, the sources should be
initialised with the help of single-qubit rotations and repeat-until-success
two-qubit quantum gates [Lim et al., Phys. Rev. Lett. 95, 030305 (2005)].
Afterwards, the state of the sources can be mapped onto the state of N newly
generated photons whenever needed.Comment: 9 pages, 3 figure
Single-qubit rotations in two-dimensional optical lattices with multiqubit addressing
Published versio
Multiphoton entanglement through a Bell multiport beam splitter
Multiphoton entanglement is an important resource for linear optics quantum
computing. Here we show that a wide range of highly entangled multiphoton
states, including W-states, can be prepared by interfering single photons
inside a Bell multiport beam splitter and using postselection. A successful
state preparation is indicated by the collection of one photon per output port.
An advantage of the Bell multiport beam splitter is that it redirects the
photons without changing their inner degrees of freedom. The described setup
can therefore be used to generate polarisation, time-bin and frequency
multiphoton entanglement, even when using only a single photon source.Comment: 8 pages, 2 figures, carefully revised version, references adde
Repeat-Until-Success quantum computing using stationary and flying qubits
We introduce an architecture for robust and scalable quantum computation
using both stationary qubits (e.g. single photon sources made out of trapped
atoms, molecules, ions, quantum dots, or defect centers in solids) and flying
qubits (e.g. photons). Our scheme solves some of the most pressing problems in
existing non-hybrid proposals, which include the difficulty of scaling
conventional stationary qubit approaches, and the lack of practical means for
storing single photons in linear optics setups. We combine elements of two
previous proposals for distributed quantum computing, namely the efficient
photon-loss tolerant build up of cluster states by Barrett and Kok [Phys. Rev.
A 71, 060310(R) (2005)] with the idea of Repeat-Until-Success (RUS) quantum
computing by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)]. This idea can be
used to perform eventually deterministic two-qubit logic gates on spatially
separated stationary qubits via photon pair measurements. Under non-ideal
conditions, where photon loss is a possibility, the resulting gates can still
be used to build graph states for one-way quantum computing. In this paper, we
describe the RUS method, present possible experimental realizations, and
analyse the generation of graph states.Comment: 14 pages, 7 figures, minor changes, references and a discussion on
the effect of photon dark counts adde
Generalised Hong-Ou-Mandel Experiments with Bosons and Fermions
The Hong-Ou-Mandel (HOM) dip plays an important role in recent linear optics
experiments. It is crucial for quantum computing with photons and can be used
to characterise the quality of single photon sources and linear optics setups.
In this paper, we consider generalised HOM experiments with bosons or
fermions passing simultaneously through a symmetric Bell multiport beam
splitter. It is shown that for even numbers of bosons, the HOM dip occurs
naturally in the coincidence detection in the output ports. In contrast,
fermions always leave the setup separately exhibiting perfect coincidence
detection. Our results can be used to verify or employ the quantum statistics
of particles experimentally.Comment: 11 pages, 2 figures, more references adde
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