共查询到20条相似文献,搜索用时 343 毫秒
1.
This paper explores continuous variable entanglement in four-wave mixing when the atomic relaxation time is comparable to and longer than the cavity relaxation time.In this case the atomic memory is included in the field correlations and the entanglement in the output fields can be significantly enhanced.Einstein-Podolsky-Rosen (EPR) entanglement is achievable even in the bad cavity limit.This shows the EPR entanglement generation without need of good cavity. 相似文献
2.
M.?E.?Ta?g?n B.??ztop M.??.?Oktel ?.?E.?Müstecapl?og?lu 《Optics and Spectroscopy》2010,108(3):433-437
Quantum correlations among atoms in superradiant Bose-Einstein condensates are discussed. It is shown that atoms in the superradiant
atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein-Podolsky-Rosen (EPR)-type quantum
correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided. 相似文献
3.
4.
According to Bell's theorem, the degree of correlation between spatially separated measurements on a quantum system is limited by certain inequalities if one assumes the condition of locality. Quantum mechanics predicts that this limit can be exceeded, making it nonlocal. We analyse the effect of an environment modelled by a fluctuating magnetic field on the quantum correlations in an EPR singlet as seen in the Bell inequality. We show that in an EPR setup, the system goes from the usual ‘violation’ of Bell's inequality to a ‘non-violation’ for times larger than a characteristic time scale which is related to the parameters of the fluctuating field. We also look at these inequalities as a function of the spatial separation between the EPR pair. 相似文献
5.
N. Cufaro-Petroni C. Dewdney P. R. Holland A. Kyprianidis J. P. Vigier 《Foundations of Physics》1987,17(8):759-773
Assuming that future experiments confirm Aspect's discovery of nonlocal interactions between quantum pairs of correlated particles, we analyze the constraints imposed by the EPR reasoning on the said interactions. It is then shown that the nonlocal relativistic quantum potential approach plainly satisfies the Einstein causality criteria as well as the energy-momentum conservation in individual microprocesses. Furthermore, this approach bypasses a new causal paradox for timelike separated EPR measurements deduced by Sutherland in the frame of an approach by means of space-time zigzags with advanced potentials. It is finally demonstrated that this inherent quantum causal direct interaction establishes permanent EPR correlations which are always restricted to spacelike separations and are instantaneous only in the center-of-mass rest frame of the two-particle system. 相似文献
6.
Jens Scheer 《Foundations of Physics Letters》1990,3(6):577-580
It is argued that the problem of causal anomalies that still may exist in Vigier's explanation of superluminal EPR type correlations may be removed in the framework of Aron's stochastic foundation of relativity. 相似文献
7.
Tirzah Kaufherr 《Foundations of Physics》1985,15(10):1043-1051
Some new aspects of the EPR paradox are considered. We first show that the authors' argument, leading to the conclusion that quantum theory is incomplete, is based on a tacit assumption that may be questioned. We then investigate the non-local features of the EPR setup and point out an interesting connection between the nonlocality involved in the quantum correlations of pairs of particles and that of a single particle in quantum theory. 相似文献
8.
While investigating quantum correlations in atomic systems, we note that single measurements contain information about these correlations. Using a simple model of measurement-analogous to the one used in quantum optics-we show how to extract higher-order correlation functions from individual "photographs" of the atomic sample. As a possible application, we apply the method to detect a subtle phase coherence in mesoscopic superpositions. 相似文献
9.
Quantum teleportation of a polarization state with a complete bell state measurement 总被引:16,自引:0,他引:16
We report a quantum teleportation experiment in which nonlinear interactions are used for the Bell state measurements. The experimental results demonstrate the working principle of irreversibly teleporting an unknown arbitrary polarization state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that all four Bell states can be distinguished in the Bell state measurement. Teleportation of a polarization state can thus occur with certainty in principle. 相似文献
10.
Walborn SP Salles A Gomes RM Toscano F Souto Ribeiro PH 《Physical review letters》2011,106(13):130402
Steering is a form of quantum nonlocality that is intimately related to the famous Einstein-Podolsky-Rosen (EPR) paradox that ignited the ongoing discussion of quantum correlations. Within the hierarchy of nonlocal correlations appearing in nature, EPR steering occupies an intermediate position between Bell nonlocality and entanglement. In continuous variable systems, EPR steering correlations have been observed by violation of Reid's EPR inequality, which is based on inferred variances of complementary observables. Here we propose and experimentally test a new criterion based on entropy functions, and show that it is more powerful than the variance inequality for identifying EPR steering. Using the entropic criterion our experimental results show EPR steering, while the variance criterion does not. Our results open up the possibility of observing this type of nonlocality in a wider variety of quantum states. 相似文献
11.
Deng Y Pandian RP Ahmad R Kuppusamy P Zweier JL 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,181(2):254-261
Magnetic field modulation in CW electron paramagnetic resonance (EPR) is used for signal detection. However, it can also distort signal lineshape. In experiments where the linewidth information is of particular importance, small modulation amplitude is usually used to limit the lineshape distortion. The use of small modulation amplitude, however, results in low signal-to-noise ratio and therefore affects the precision of linewidth measurements. Recently, a new spectral simulation model has been developed enabling accurate fitting of modulation-broadened EPR spectra in liquids. Since the use of large modulation amplitude (over-modulation) can significantly enhance the EPR signal, the precision of linewidth measurements is therefore greatly improved. We investigated the over-modulation technique in EPR oximetry experiments using the oxygen-sensing probe lithium octa-n-butoxy-substitued naphthalocyanine (LiNc-BuO). Modulation amplitudes 2-18 times the intrinsic linewidth of the probe were applied to increase the spectral signal-to-noise ratio. The intrinsic linewidth of the probe at different oxygen concentrations was accurately extracted through curve fitting from the enhanced spectra. Thus, we demonstrated that the over-modulation model is also applicable to particulate oxygen-sensing probes such as LiNc-BuO and that the lineshape broadening induced by oxygen is separable from that induced by over-modulation. Therefore, the over-modulation technique can be used to enhance sensitivity and improve linewidth measurements for EPR oximetry with particulate oxygen-sensing probes with Lorentzian lineshape. It should be particularly useful for in vivo oxygen measurements, in which direct linewidth measurements may not be feasible due to inadequate signal-to-noise ratio. 相似文献
12.
Considering the common cause principle, we construct a local-contextual hidden-variable model for the Bohm version of EPR experiment. Our proposed model can reproduce the predictions of quantum mechanics. It can be also extended to classical examples in which similar correlations may be revealed. 相似文献
13.
We show that pair correlations may play an important role in the dynamical properties of a Bose-Einstein condensed gas composed of an atomic field resonantly coupled with a condensed field of molecular dimers. Specifically, pair correlations in this system can dramatically modify the coherent and incoherent transfers between the atomic and molecular fields. 相似文献
14.
C. S. Unnikrishnan 《Optics and Spectroscopy》2001,91(3):393-398
The Einstein-Podolsky-Rosen (EPR) nonlocality puzzle has been recognized as one of the most important unresolved issues in the foundational aspects of quantum mechanics. We show that the problem is more or less entirely resolved, if the quantum correlations are calculated directly from local quantities, which preserve the phase information in the quantum system. We assume strict locality for the probability amplitudes instead of local realism for the outcomes and calculate an amplitude correlation function. Then the experimentally observed correlation of outcomes is calculated from the square of the amplitude correlation function. Locality of amplitudes implies that measurement on one particle does not collapse the companion particle to a definite state. Apart from resolving the EPR puzzle, this approach shows that the physical interpretation of apparently “nonlocal” effects, such as quantum teleportation and entanglement swapping, are different from what is usually assumed. Bell-type measurements do not change distant states. Yet the correlations are correctly reproduced, when measured, if complex probability amplitudes are treated as the basic local quantities. As examples, we derive the quantum correlations of two-particle maximally entangled states and the three-particle Greenberger-Horne-Zeilinger entangled state. 相似文献
15.
In vivo electron paramagnetic resonance (EPR) has been very useful for studies in animals, and these results suggest that
there are some very attractive potential applications in human subjects. In this article, we describe our rationale for the
clinical application of in vivo EPR, some of the principal technical challenges, the initial results in human subjects, and
our evaluation of the areas where in vivo EPR is likely to play an important clinical role in the near future. The most obvious
area of very high potential for clinical applications is tissue oximetry, where in vivo EPR can provide repeated and accurate
measurements of tissue pO2, a type of measurement that cannot be obtained by other techniques. Oximetry is capable of providing clinicians with information
that can impact directly on diagnosis and therapy, especially for peripheral vascular disease, oncology, and wound healing.
The other area of great immediate importance is the ability of in vivo EPR to measure clinically significant exposures to
ionizing radiation after the fact, which may occur due to accidents, terrorist activity, or nuclear war. The results obtained
already from human subjects demonstrate the feasibility of the use of in vivo EPR for measurements in human subjects. We anticipate
that in vivo EPR will play a vital role in the clinical management of various pathologies in the years to come. 相似文献
16.
Zi-Wei Li Zhi-Hua Guo Huai-Xin Cao 《International Journal of Theoretical Physics》2018,57(11):3285-3295
Einstein-Podolsky-Rosen(EPR) steering is one of important quantum correlations of a composite quantum system, which was observed firstly by Schrödinger in the context of the famous EPR paradox and has been discussed recently. In this paper, we give some characterizations of EPR steerability of bipartite states by proving some necessary and sufficient conditions for a state to be unsteerable with a measurement assemblage of Alice. Based on one of the obtained characterizations, we derive an EPR steering inequality, which serves to check EPR steerability of the maximally entangled states. 相似文献
17.
《Radiation measurements》2009,44(1):6-10
There is now an increased need for accident dosimetry due to the increased risk of significant exposure to ionizing radiation from terrorism or accidents. In such scenarios, dose measurements should be made in individuals rapidly and with sufficient accuracy to enable effective triage. Electron paramagnetic resonance (EPR) is a physical method of high potential for meeting this need, providing direct measurements of the radiation-induced radicals, which are unambiguous signatures of exposure to ionizing radiation. For individual retrospective dosimetry, EPR in tooth enamel is a proven and effective technique when isolated teeth can be obtained. There are some promising developments that may make these measurements feasible without the need to remove the teeth, but their field applicability remains to be demonstrated. However, currently it is difficult under emergency conditions to obtain tooth enamel in sufficient amounts for accurate dose measurements. Since fingernails are much easier to sample, they can be used in potentially exposed populations to determine if they were exposed to life-threatening radiation doses. Unfortunately, only a few studies have been carried out on EPR radiation-induced signals in fingernails, and, while there are some promising aspects, the reported results were generally inconclusive. In this present paper, we report the results of a systematic investigation of the potential use of fingernails as retrospective radiation dosimeters. 相似文献
18.
Yokoyama H 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2012,214(1):119-123
Direct irradiation of a sample using a quartz oscillator operating at 250 MHz was performed for EPR measurements. Because a quartz oscillator is a frequency fixed oscillator, the operating frequency of an EPR resonator (loop-gap type) was tuned to that of the quartz oscillator by using a single-turn coil with a varactor diode attached (frequency shift coil). Because the frequency shift coil was mobile, the distance between the EPR resonator and the coil could be changed. Coarse control of the resonant frequency was achieved by changing this distance mechanically, while fine frequency control was implemented by changing the capacitance of the varactor electrically. In this condition, EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) were made. To compare the presented method with a conventional method, the EPR measurements were also done by using a synthesizer at the same EPR frequency. In the conventional method, the noise level increased at high irradiation power. Because such an increase in the noise was not observed in the presented method, high sensitivity was obtained at high irradiation power. 相似文献
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20.
M. Heidari Saani H. Hashemi A. Ranjbar M. A. Vesaghi A. Shafiekhani 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(2):219-223
The relationship between unpaired electron delocalization and nearest-neighbor atomic relaxations in the vacancies of diamond
has been determined in order to understand the microscopic reason behind the neighboring atomic relaxation. The Density Functional
Theory (DFT) cluster method is applied to calculate the single-electron wavefunction of the vacancy in different charge states.
Depending on the charge and spin state of the vacancies, at outward relaxations, 84-90% of the unpaired electron densities
are localized on the first neighboring atoms. The calculated spin localizations on the first neighboring atoms in the ground
state of the negatively charged vacancy and in the spin quintet excited state of the neutral vacancy are in good agreement
with Electron Paramagnetic Resonance (EPR) measurements. The calculated spin localization of the positively charged vacancy
contrasts with the tentative assignment of the NIRIM-3 EPR signal to this center in (p-type) semiconductor diamond. The sign
of the lattice relaxation in the diamond vacancy is explained based on the effect of electron delocalization on nearest-neighbor
ion-ion screening, and also its effect on the bond length of neighboring atoms. 相似文献