422 research outputs found
Motion-light parametric amplifier and entanglement distributor
We propose a scheme for entangling the motional mode of a trapped atom with a
propagating light field via a cavity-mediated parametric interaction. We then
show that if this light field is subsequently coupled to a second distant atom
via a cavity-mediated linear-mixing interaction, it is possible to transfer the
entanglement from the light beam to the motional mode of the second atom to
create an EPR-type entangled state of the positions and momenta of two
distantly-separated atoms.Comment: 9 pages, 8 figures, REVTe
Using dark modes for high-fidelity optomechanical quantum state transfer
In a recent publication [Y.D. Wang and A.A. Clerk, Phys. Rev. Lett. 108,
153603 (2012)], we demonstrated that one can use interference to significantly
increase the fidelity of state transfer between two electromagnetic cavities
coupled to a common mechanical resonator over a naive sequential-transfer
scheme based on two swap operations. This involved making use of a delocalized
electromagnetic mode which is decoupled from the mechanical resonator, a
so-called "mechanically-dark" mode. Here, we demonstrate the existence of a new
"hybrid" state transfer scheme which incorporates the best elements of the
dark-mode scheme (protection against mechanical dissipation) and the
double-swap scheme (fast operation time). Importantly, this new scheme also
does not require the mechanical resonator to be prepared initially in its
ground state. We also provide additional details on the previously-described
interference-enhanced transfer schemes, and provide an enhanced discussion of
how the interference physics here is intimately related to the optomechanical
analogue of electromagnetically-induced transparency (EIT). We also compare the
various transfer schemes over a wide range of relevant experimental parameters,
producing a "phase diagram" showing the the optimal transfer scheme for
different points in parameter space.Comment: 39 pages, 11 figures NJP 14 (Focus issue on Optomechanics
Thermal Properties of Interacting Bose Fields and Imaginary-Time Stochastic Differential Equations
Matsubara Green's functions for interacting bosons are expressed as classical
statistical averages corresponding to a linear imaginary-time stochastic
differential equation. This makes direct numerical simulations applicable to
the study of equilibrium quantum properties of bosons in the non-perturbative
regime. To verify our results we discuss an oscillator with quartic
anharmonicity as a prototype model for an interacting Bose gas. An analytic
expression for the characteristic function in a thermal state is derived and a
Higgs-type phase transition discussed, which occurs when the oscillator
frequency becomes negative.Comment: Published versio
Unusual light spectra from a two-level atom in squeezed vacuum
We investigate the interaction of an atom with a multi-channel squeezed
vacuum. It turns out that the light coming out in a particular channel can have
anomalous spectral properties, among them asymmetry of the spectrum, absence of
the central peak as well as central hole burning for particular parameters. As
an example plane-wave squeezing is considered. In this case the above phenomena
can occur for the light spectra in certain directions. In the total spectrum
these phenomena are washed out.Comment: 16 pages, LaTeX, 3 figures (included via epsf
Bifurcation Phenomenon in a Spin Relaxation
Spin relaxation in a strong-coupling regime (with respect to the spin system)
is investigated in detail based on the spin-boson model in a stochastic limit.
We find a bifurcation phenomenon in temperature dependence of relaxation
constants, which is never observed in the weak-coupling regime. We also discuss
inequalities among the relaxation constants in our model and show the
well-known relation 2\Gamma_T >= \Gamma_L, for example, for a wider parameter
region than before.Comment: REVTeX4, 5 pages, 5 EPS figure
Determinants of anti-vascular action by combretastatin A-4 phosphate: role of nitric oxide
The anti-vascular action of the tubulin binding agent combretastatin A-4 phosphate (CA-4-P) has been quantified in two types of murine tumour, the breast adenocarcinoma CaNT and the round cell sarcoma SaS. The functional vascular volume, assessed using a fluorescent carbocyanine dye, was significantly reduced at 18 h after CA-4-P treatment in both tumour types, although the degree of reduction was very different in the two tumours. The SaS tumour, which has a higher nitric oxide synthase (NOS) activity than the CaNT tumour, showed ~10-fold greater resistance to vascular damage by CA-4-P. This is consistent with our previous findings, which showed that NO exerts a protective action against this drug. Simultaneous administration of CA-4-P with a NOS inhibitor, Nω-nitro-L-arginine (L-NNA), resulted in enhanced vascular damage and cytotoxicity in both tumour types. Administration of diethylamine NO, an NO donor, conferred protection against the vascular damaging effects. Following treatment with CA-4-P, neutrophil infiltration into the tumours, measured by myeloperoxidase (MPO) activity, was significantly increased. Levels of MPO activity also correlated with the levels of vascular injury and cytotoxicity measured in both tumour types. Neutrophilic MPO generates free radicals and may therefore contribute to the vascular damage associated with CA-4-P treatment. MPO activity was significantly increased in the presence of L-NNA, suggesting that the protective effect of NO against CA-4-P-induced vascular injury may be, at least partially, mediated by limiting neutrophil infiltration. The data are consistent with the hypothesis that neutrophil action contributes to vascular injury by CA-4-P and that NO generation acts to protect the tumour vasculature against CA4-P-induced injury. The protective effect of NO is probably associated with an anti-neutrophil action. © 2000 Cancer Research Campaig
Squeezing generation and revivals in a cavity-ion system in contact with a reservoir
We consider a system consisting of a single two-level ion in a harmonic trap,
which is localized inside a non-ideal optical cavity at zero temperature and
subjected to the action of two external lasers. We are able to obtain an
analytical solution for the total density operator of the system and show that
squeezing in the motion of the ion and in the cavity field is generated. We
also show that complete revivals of the states of the motion of the ion and of
the cavity field occur periodically.Comment: 9 pages, 3 figure
Electroporation of human microvascular endothelial cells: evidence for an anti-vascular mechanism of electrochemotherapy
Recent studies have indicated that the antitumour effectiveness of electrochemotherapy, a combination of chemotherapeutic drugs with application of high voltage electric pulses applied to the tumour nodule (electroporation), result in a significant reduction in tumour blood flow and may therefore be mediated by an anti-vascular mechanism. The aim of this study was to evaluate the cytotoxicity of electroporation with bleomycin or cisplatin on cultured human microvascular endothelial cells (HMEC-1). The sensitivity of HMEC-1 cells to a 5 min treatment by electroporation with bleomycin or cisplatin (8 electric pulses, pulse duration 100 μs, frequency 1 Hz, electric field intensity 1400 V cm–1) was compared to the sensitivity of cells treated continuously for 3 days with drugs alone. HMEC-1 cells were moderately sensitive to continuous exposure to cisplatin, but showed greater sensitivity to bleomycin. Combination of a 5 min drug exposure with electric pulses increased cytotoxicity of cisplatin by ∼10-fold for cisplatin and ∼5000-fold for bleomycin. The electroporation of HMEC-1 cells with bleomycin for a 5 min exposure was ∼250-fold better than a continuous exposure to the drug alone. The results of this study indicate that the anti-tumour action of electrochemotherapy is likely to be due, in part, to the highly sensitive response of vascular endothelial cells. Further studies are necessary to identify the determinants of endothelial response and its relationship to the anti-vascular action of electrochemotherapy in vivo. © 2001 Cancer Research Campaign http://www.bjcancer.co
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