314 research outputs found
All-optical generation of states for "Encoding a qubit in an oscillator"
Both discrete and continuous systems can be used to encode quantum
information. Most quantum computation schemes propose encoding qubits in
two-level systems, such as a two-level atom or an electron spin. Others exploit
the use of an infinite-dimensional system, such as a harmonic oscillator. In
"Encoding a qubit in an oscillator" [Phys. Rev. A 64 012310 (2001)], Gottesman,
Kitaev, and Preskill (GKP) combined these approaches when they proposed a
fault-tolerant quantum computation scheme in which a qubit is encoded in the
continuous position and momentum degrees of freedom of an oscillator. One
advantage of this scheme is that it can be performed by use of relatively
simple linear optical devices, squeezing, and homodyne detection. However, we
lack a practical method to prepare the initial GKP states. Here we propose the
generation of an approximate GKP state by using superpositions of optical
coherent states (sometimes called "Schr\"odinger cat states"), squeezing,
linear optical devices, and homodyne detection.Comment: 4 pages, 3 figures. Submitted to Optics Letter
Quantum state conversion by cross-Kerr interaction
A generalized Mach-Zehnder-type interferometer equipped with cross-Kerr
elements is proposed to convert N-photon truncated single-mode quantum states
into (N+1)-mode single-photon states, which are suitable for further state
manipulation by means of beam splitter arrays and ON/OFF-detections, and vice
versa. Applications to the realization of unitary and non-unitary
transformations, quantum state reconstruction, and quantum telemanipulation are
studied.Comment: 22 pages, 4 figures, using a4.st
Intelligent Financial Fraud Detection Practices: An Investigation
Financial fraud is an issue with far reaching consequences in the finance
industry, government, corporate sectors, and for ordinary consumers. Increasing
dependence on new technologies such as cloud and mobile computing in recent
years has compounded the problem. Traditional methods of detection involve
extensive use of auditing, where a trained individual manually observes reports
or transactions in an attempt to discover fraudulent behaviour. This method is
not only time consuming, expensive and inaccurate, but in the age of big data
it is also impractical. Not surprisingly, financial institutions have turned to
automated processes using statistical and computational methods. This paper
presents a comprehensive investigation on financial fraud detection practices
using such data mining methods, with a particular focus on computational
intelligence-based techniques. Classification of the practices based on key
aspects such as detection algorithm used, fraud type investigated, and success
rate have been covered. Issues and challenges associated with the current
practices and potential future direction of research have also been identified.Comment: Proceedings of the 10th International Conference on Security and
Privacy in Communication Networks (SecureComm 2014
Schrodinger cats and their power for quantum information processing
We outline a toolbox comprised of passive optical elements, single photon
detection and superpositions of coherent states (Schrodinger cat states). Such
a toolbox is a powerful collection of primitives for quantum information
processing tasks. We illustrate its use by outlining a proposal for universal
quantum computation. We utilize this toolbox for quantum metrology
applications, for instance weak force measurements and precise phase
estimation. We show in both these cases that a sensitivity at the Heisenberg
limit is achievable.Comment: 10 pages, 5 figures; Submitted to a Special Issue of J. Opt. B on
"Fluctuations and Noise in Photonics and Quantum Optics" (Herman Haus
Memorial Issue
Optimal purification of thermal graph states
In this paper, a purification protocol is presented and its performance is
proven to be optimal when applied to a particular subset of graph states that
are subject to local Z-noise. Such mixed states can be produced by bringing a
system into thermal equilibrium, when it is described by a Hamiltonian which
has a particular graph state as its unique ground state. From this protocol, we
derive the exact value of the critical temperature above which purification is
impossible, as well as the related optimal purification rates. A possible
simulation of graph Hamiltonians is proposed, which requires only bipartite
interactions and local magnetic fields, enabling the tuning of the system
temperature.Comment: 5 pages, 4 figures v2: published versio
Superradiance and Phase Multistability in Circuit Quantum Electrodynamics
By modeling the coupling of multiple superconducting qubits to a single
cavity in the circuit-quantum electrodynamics (QED) framework we find that it
should be possible to observe superradiance and phase multistability using
currently available technology. Due to the exceptionally large couplings
present in circuit-QED we predict that superradiant microwave pulses should be
observable with only a very small number of qubits (just three or four), in the
presence of energy relaxation and non-uniform qubit-field coupling strengths.
This paves the way for circuit-QED implementations of superradiant state
readout and decoherence free subspace state encoding in subradiant states. The
system considered here also exhibits phase multistability when driven with
large field amplitudes, and this effect may have applications for collective
qubit readout and for quantum feedback protocols.Comment: Published Versio
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