161 research outputs found
Intracavity weak nonlinear phase shifts with single photon driving
We investigate a doubly resonant optical cavity containing a Kerr nonlinear
medium that couples two modes by a cross phase modulation. One of these modes
is driven by a single photon pulsed field, and the other mode is driven by a
coherent state. We find an intrinsic phase noise mechanism for the cross phase
shift on the coherent beam which can be attributed to the random emission times
of single photons from the cavity. An application to a weak nonlinearity phase
gate is discussed
Overcoming decoherence in the collapse and revival of spin Schrodinger-cat states
In addition to being a very interesting quantum phenomenon, Schrödinger-cat-state swapping has the potential for application in the preparation of quantum states that could be used in metrology and other quantum processing. We study in detail the effects of field decoherence on a Schrödinger-cat-state-swapping system comprising a set of identical qubits, or spins, all coupled to a field mode. We demonstrate that increasing the number of spins actually mitigates the effects of field decoherence on the collapse and revival of a spin Schrödinger-cat state, which could be of significant utility in quantum metrology and other quantum processing
Quantum measurement and the quantum to classical transition in a non-linear quantum oscillator
We study a non-linear quantum mechanical oscillator, acting as a measurement device. Candidate systems for realising such apparatus range from superconducting devices through to nano-mechanical resonators. The measurement device comprises an oscillator circuit where the dynamics of expectation values, in its correspondence limit, are either chaotic-like or periodic depending on the measured state of the quantum object – in this case a qubit. In a previous work we showed how the classical like trajectories of such a quantum system can act as a model of a projective measurement process. Here we investigate the quantum to classical transition of the measurement device and postulate criteria for realisation of an effective implementation of such a device
Quantum-classical crossover of a field mode
We explore the quantum-classical crossover in the behaviour of a quantum field mode. The quantum behaviour
of a two-state system—a qubit—coupled to the field is used as a probe. Collapse and revival of the
qubit inversion form the signature for quantum behaviour of the field and continuous Rabi oscillations form the
signature for classical behaviour of the field. We demonstrate both limits in a single model for the full coupled
system, for field states with the same average field strength, and so for qubits with the same Rabi frequency
A bibliography of the giant clams (Bivalvia: Tridacnidae)
Clam fisheries, Clam culture, Bibliographies Tridacnidae
Maximal Violation of Bell Inequalities using Continuous Variables Measurements
We propose a whole family of physical states that yield a violation of the
Bell CHSH inequality arbitrarily close to its maximum value, when using
quadrature phase homodyne detection. This result is based on a new binning
process called root binning, that is used to transform the continuous variables
measurements into binary results needed for the tests of quantum mechanics
versus local realistic theories. A physical process in order to produce such
states is also suggested. The use of high-efficiency spacelike separated
homodyne detections with these states and this binning process would result in
a conclusive loophole-free test of quantum mechanics.Comment: 7 pages, 5 figures, to appear in PRA in a slightly different versio
Optimal States for Bell inequality Violations using Quadrature Phase Homodyne Measurements
We identify what ideal correlated photon number states are to required to
maximize the discrepancy between local realism and quantum mechanics when a
quadrature homodyne phase measurement is used. Various Bell inequality tests
are considered.Comment: 6 pages, 5 Figure
Wigner Functions for Arbitrary Quantum Systems
The possibility of constructing a complete, continuous Wigner function for any quantum system has been a subject of investigation for over 50 years. A key system that has served to illustrate the difficulties of this problem has been an ensemble of spins. While numerous attempts have come close to generating a complete Wigner phase-space description for such a system, each has either been artificial in its construction or restricted in its applications. Here we present a general method of constructing Wigner functions that can be used to fully describe quantum spin systems of any
dimension or ensemble size
Efficient Quantum Computation using Coherent States
Universal quantum computation using optical coherent states is studied. A
teleportation scheme for a coherent-state qubit is developed and applied to
gate operations. This scheme is shown to be robust to detection inefficiency.Comment: 6 pages, 5 figures, extended and modified (in print, PRA
Nonclassicality and information exchange in deterministic entanglement formation
We discuss the role of nonclassicality of quantum states as a necessary
resource in deterministic generation of multipartite entangled states. In
particular for three bilinearly coupled modes of the electromagnetic field,
tuning of the coupling constants between the parties allows the total system to
evolve into both Bell and GHZ states only when one of the parties is initially
prepared in a nonclassical state. A superposition resource is then converted
into an entanglement resource.Comment: Replaced by the accepted version. Two optical implementations of the
quantum resource conversion protocol are now proposed. To appear in Phys.
Lett. A. 7 pages, 1 figur
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