10,446 research outputs found
Visualizing the Quantum Interaction Picture in Phase Space
We illustrate the correspondence between the quantum Interaction
Picture-evolution of the state of a quantum system in Hilbert space and a
combination of local and global transformations of its Wigner function in phase
space. To this aim, we consider the time-evolution of a quantized harmonic
oscillator driven by both a linear and a quadratic (in terms of bosonic
creation and annihilation operators) potentials and employ the Magnus series to
derive the exact form of the time-evolution operator. In this case, the
Interaction Picture corresponds to a local transformation of phase
space-reference frame into the one that is co-moving with the Wigner function.Comment: Submitted to New Journal of Physic
Dependence of the evolution of the cavity radiation of a coherently pumped correlated emission laser on dephasing and phase fluctuation
Analysis of the dynamics of the cavity radiation of a coherently pumped
correlated emission laser is presented. The phase fluctuation and dephasing are
found to affect the time evolution of the two-mode squeezing and intensity of
the cavity radiation significantly. The intensity and degree of the two-mode
squeezing increase at early stages of the process with time, but this trend
changes rapidly afterwards. It is also shown that they increase with phase
fluctuation and dephasing in the strong driving limit, however the situation
appears to be opposite in the weak driving limit. This essentially suggests
that the phase fluctuation and dephasing weaken the coherence induced by a
strong driving mechanism so that the spontaneous emission gets a chance. The
other important aspect of the phase fluctuation, in this regard, is the
relaxation of the time at which the maximum squeezing is manifested as well as
the time in which the radiation remains in a squeezed state.Comment: 10 pages, 12 figure
Frictional quantum decoherence
The dynamics associated with a measurement-based master equation for quantum
Brownian motion are investigated. A scheme for obtaining time evolution from
general initial conditions is derived. This is applied to analyze dissipation
and decoherence in the evolution of both a Gaussian and a Schr\"{o}dinger cat
initial state. Dependence on the diffusive terms present in the master equation
is discussed with reference to both the coordinate and momentum
representations.Comment: 18 pages, 7 figure
On the Quantum Phase Operator for Coherent States
In papers by Lynch [Phys. Rev. A41, 2841 (1990)] and Gerry and Urbanski
[Phys. Rev. A42, 662 (1990)] it has been argued that the phase-fluctuation
laser experiments of Gerhardt, B\"uchler and Lifkin [Phys. Lett. 49A, 119
(1974)] are in good agreement with the variance of the Pegg-Barnett phase
operator for a coherent state, even for a small number of photons. We argue
that this is not conclusive. In fact, we show that the variance of the phase in
fact depends on the relative phase between the phase of the coherent state and
the off-set phase of the Pegg-Barnett phase operator. This off-set
phase is replaced with the phase of a reference beam in an actual experiment
and we show that several choices of such a relative phase can be fitted to the
experimental data. We also discuss the Noh, Foug\`{e}res and Mandel [Phys.Rev.
A46, 2840 (1992)] relative phase experiment in terms of the Pegg-Barnett phase
taking post-selection conditions into account.Comment: 8 pages, 8 figures. Typographical errors and misprints have been
corrected. The outline of the paper has also been changed. Physica Scripta
(in press
Two-mode entanglement in two-component Bose-Einstein condensates
We study the generation of two-mode entanglement in a two-component
Bose-Einstein condensate trapped in a double-well potential. By applying the
Holstein-Primakoff transformation, we show that the problem is exactly solvable
as long as the number of excitations due to atom-atom interactions remains low.
In particular, the condensate constitutes a symmetric Gaussian system, thereby
enabling its entanglement of formation to be measured directly by the
fluctuations in the quadratures of the two constituent components [Giedke {\it
et al.}, Phys. Rev. Lett. {\bf 91}, 107901 (2003)]. We discover that
significant two-mode squeezing occurs in the condensate if the interspecies
interaction is sufficiently strong, which leads to strong entanglement between
the two components.Comment: 22 pages, 4 figure
Number operator-annihilation operator uncertainty as an alternative of the number-phase uncertainty relation
We consider a number operator-annihilation operator uncertainty as a well
behaved alternative to the number-phase uncertainty relation, and examine its
properties. We find a formulation in which the bound on the product of
uncertainties depends on the expectation value of the particle number. Thus,
while the bound is not a constant, it is a quantity that can easily be
controlled in many systems. The uncertainty relation is approximately saturated
by number-phase intelligent states. This allows us to define amplitude
squeezing, connecting coherent states to Fock states, without a reference to a
phase operator. We propose several setups for an experimental verification.Comment: 8 pages including 3 figures, revtex4; v2: typos corrected,
presentation improved; v3: presentation considerably extended; v4: published
versio
Mach-Zehnder Interferometry at the Heisenberg Limit with coherent and squeezed-vacuum light
We show that the phase sensitivity of a Mach-Zehnder
interferometer fed by a coherent state in one input port and squeezed-vacuum in
the other one is i) independent from the true value of the phase shift and ii)
can reach the Heisenberg limit , where is the
average number of particles of the input states. We also show that the
Cramer-Rao lower bound, , can be saturated for arbitrary values of the squeezing parameter
and the amplitude of the coherent mode by a Bayesian phase
inference protocol.Comment: 4 pages, 4 figure
Fidelity and the communication of quantum information
We compare and contrast the error probability and fidelity as measures of the quality of the receiver's measurement strategy for a quantum communications system. The error probability is a measure of the ability to retrieve classical information and the fidelity measures the retrieval of quantum information. We present the optimal measurement strategies for maximizing the fidelity given a source that encodes information on the symmetric qubit-states
Decoherence due to three-body loss and its effect on the state of a Bose-Einstein condensate
A Born-Markov master equation is used to investigate the decoherence of the
state of a macroscopically occupied mode of a cold atom trap due to three-body
loss. In the large number limit only coherent states remain pure for times
longer than the decoherence time: the time it takes for just three atoms to be
lost from the trap. For large numbers of atoms (N>10^4) the decoherence time is
found to be much faster than the phase collapse time caused by intra-trap
atomic collisions
Nano-Scale Hydroxyapatite: Synthesis, Two-Dimensional Transport Experiments, and Application for Uranium Remediation
Synthetic nano-scale hydroxyapatite (NHA) was prepared and characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The XRD data confirmed that the crystalline structure and chemical composition of NHA correspond to Ca5OH(PO4)3. The SEM data confirmed the size of NHA to be less than 50 nm. A two-dimensional physical model packed with saturated porous media was used to study the transport characteristics of NHA under constant flow conditions. The data show that the transport patterns of NHA were almost identical to tracer transport patterns. This result indicates that the NHA material can move with water like a tracer, and its movement was neither retarded nor influenced by any physicochemical interactions and/or density effects. We have also tested the reactivity of NHA with 1 mg/L hexavalent uranium (U(VI)) and found that complete removal of U(VI) is possible using 0.5 g/L NHA at pH 5 to 6. Our results demonstrate that NHA has the potential to be injected as a dilute slurry for in situ treatment of U(VI)-contaminated groundwater systems
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