摘要:

Experiments have shown that individual photons penetrate an optical tunnel barrier with an effective group velocity considerably greater than the vacuum speed of light. The experiments were conducted with a two-photon parametric down-conversion light source, which produced correlated, but random, emissions of photon pairs. The two photons of a given pair were emitted in slightly different directions so that one photon passed through the tunnel barrier, while the other photon passed through the vacuum. The time delay for the tunneling photon relative to its twin was measured by adjusting the path length difference between the two photons in a Hong-Ou-Mandel interferometer, in order to achieve coincidence detection. We found that the photon transit time through the barrier was smaller than the twin photon’s transit time through an equal distance in vacuum, indicating that the process of tunneling in quantum mechanics is superluminal. Various conflicting theories of tunneling times are compared with experiment. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57888

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Signals conveyed by evanescent modes can travel faster than light. Some special features of signals are introduced and it is shown that frequency band limitation of signals is a fundamental property. Evanescent modes are characterized by extraordinary properties: Their energy isnegative, they are not directly measurable, and the evanescent region is not causal since the modes traverse this region instantaneously. The study demonstrates the necessity of quantum mechanics in order to understand the superluminal signal velocity of apparently classical evanescent modes. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57848

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Some recent experiments, performed at Berkeley, Cologne, Florence and Vienna led to the claim that something seems to travel with a speed larger than the speedcof light in vacuum. Various other experimental results seem to point in the same direction: For instance, localized wavelet-type solutions of Maxwell equations have been found, both theoretically and experimentally, that travel with Superluminal speed. Even muonic and electronic neutrions—it has been proposed—might be “tachyons”, since their square mass appears to be negative; not to mention the apparent Superluminal expansions observed in the core of quasars and, recently, in the so-called galactic microquasars. Nevertheless, all such data or results donotplace relativistic causality in jeopardy. For instance, it is possible (at least in microphysics) to solve also the known causal paradoxes, devised for “faster than light” motion, even if this is not widely recognized. Here we show, in detail and rigorously, how to solve the oldest causal paradox, originally proposed by Tolman, which is the kernel of many further tachyon paradoxes. The key to the solution is a careful application of tachyon mechanics, as it unambiguously follows from Special Relativity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57872

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Although the now well-established fact of superluminal tunneling may be somewhat surprising, we maintain that as in previous cases of quantum nonlocality, there is in fact no paradox. No signal, in the sense of previously unpredictable information, may be transmitted faster thancby making use of anomalously fast tunneling. On the other hand, we believe that mysteries persist aboutwherea particle is while it is tunneling, howlongit spends there, and whether (in a carefully defined sense, but less restricted than that of the familiar two-slit discussions) it can bein two placesat the same time. We are setting up a series of atom optics experiments which we believe will provide direct experimental evidence about some of these issues. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57849

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The nonlocal aspects of Einstein-Podolsky-Rosen correlations are commonly regarded as a strong indication that quantum mechanics is a nonlocal theory. We disagree with this conclusion and argue in favor of the view that these correlations can be understood in terms of local physics. In particular, all features of quantum erasure—a procedure that exploits the nonlocal quantum correlations extensively—result from local actions. The classical notion of locality remains valid, but the concept of reality needs to be refined. Only those properties of quantum objects that can be verified in control experiments should be regarded as real. Further, everything can be viewed from the perspective of the time-symmetric two-state formalism, which is Lorentz covariant by construction and has no room for nonlocal elements. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57850

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Interference may occur whenever there are two or more paths or processes leading to the same final outcome, and these are in principle indistinguishable. If one of these paths becomes labeled, yielding “which-path” information, interference will vanish. However, an appropriate measurement that “erases” the distinguishability may recover interference. Remarkably, it can be recovered even in situations where there was no which-path information to erase! Using single photons in a modified Mach-Zehnder interferometer, we have investigated the various conditions that allow, prevent, and recover interference, for a variety of pure, mixed, and partially-mixed input states. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57889

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In this paper I define the terms “force-free” and “momentum change” and show that a force-free momentum change is possible in quantum mechanics. An old example of this, the Aharonov-Bohm effect, is discussed. I use Bohmian mechanics to give an “explanation” of this effect, which has the advantage of supplying a physical picture of the dynamics. By considering quantum erasers, I show that the concept of force-free momentum change can be applied to which-path measurements. Building on this I derive a new measurement-disturbance relation for two-slit interferometry. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57890

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

I start from the observation that the usual treatment of the object and the apparatus as independent systems in discussions of the quantum measurement process is not obviously consistent with a field theoretic picture. In such connection I consider a non relativistic second quantization model in which the role of the object is played by a particle out of the sea of the other particles in a macroscopic equilibrium state of the global system and the role of the apparatus index by the number of ions produced in certain given regions. In the framework of a formalism developed in preceding papers and in connection with the problem of decoherence, I also consider a specific, even if rather artificial, prescription to introduce a formal continuous monitoring of the particle distribution functions which would give an objective character to the macroscopic variables. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57891

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We consider a recent proposal aimed to overcome the conceptual difficulties of standard quantum mechanics and we review some proposed interpretations for it. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57867

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We propose a novel approach to intrinsic decoherence without adding new assumptions to standard Quantum Mechanics. We generalize the Liouville equation just by requiring the dynamical semigroup property of time evolution and dropping the unitarity requirement. With no approximations and specific statistical assumptions we find a generalized Liouville equation which depends on two characteristic time&tgr;1and&tgr;2and reduces to the usual equation in the limit&tgr;1=&tgr;2→0.However, for&tgr;1and&tgr;2arbitrarily small but finite, our equation can be written as a finite difference equation which predicts state reduction to the diagonal form in the energy representation. The rate of decoherence becomes faster at the macroscopic limit as the energy scale of the system increases. In our approach the evolution time appears, a posteriori, as a statistical variableas iftime evolution would take place randomly at average intervals&tgr;2,each evolution having a time width&tgr;1.A generalized Tam Mandelstam inequality is derived. The relation with previous work by Milburn is discussed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57868

出版商:AIP    

年代:1999

数据来源: AIP