dorsal/arxiv
View SchemaQuantum Noise and Superluminal Propagation
| Authors | Bilha Segev, Peter W. Milonni, James F. Babb, Raymond Y. Chiao |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/0004047 |
| URL | https://arxiv.org/abs/quant-ph/0004047 |
| DOI | 10.1103/PhysRevA.62.022114 |
| Journal | Phys. Rev. A 62, 022114 (2000) |
Abstract
Causal "superluminal" effects have recently been observed and discussed in various contexts. The question arises whether such effects could be observed with extremely weak pulses, and what would prevent the observation of an "optical tachyon." Aharonov, Reznik, and Stern (ARS) [Phys. Rev. Lett., vol. 81, 2190 (1998)] have argued that quantum noise will preclude the observation of a superluminal group velocity when the pulse consists of one or a few photons. In this paper we reconsider this question both in a general framework and in the specific example, suggested by Chiao, Kozhekin, and Kurizki [Phys. Rev. Lett., vol. 77, 1254 (1996)], of off-resonant, short-pulse propagation in an optical amplifier. We derive in the case of the amplifier a signal-to-noise ratio that is consistent with the general ARS conclusions when we impose their criteria for distinguishing between superluminal propagation and propagation at the speed c. However, results consistent with the semiclassical arguments of CKK are obtained if weaker criteria are imposed, in which case the signal can exceed the noise without being "exponentially large." We show that the quantum fluctuations of the field considered by ARS are closely related to superfluorescence noise. More generally we consider the implications of unitarity for superluminal propagation and quantum noise and study, in addition to the complete and truncated wavepackets considered by ARS, the residual wavepacket formed by their difference. This leads to the conclusion that the noise is mostly luminal and delayed with respect to the superluminal signal. In the limit of a very weak incident signal pulse, the superluminal signal will be dominated by the noise part, and the signal-to-noise ratio will therefore be very small.
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"abstract": "Causal \"superluminal\" effects have recently been observed and discussed in\nvarious contexts. The question arises whether such effects could be observed\nwith extremely weak pulses, and what would prevent the observation of an\n\"optical tachyon.\" Aharonov, Reznik, and Stern (ARS) [Phys. Rev. Lett., vol.\n81, 2190 (1998)] have argued that quantum noise will preclude the observation\nof a superluminal group velocity when the pulse consists of one or a few\nphotons. In this paper we reconsider this question both in a general framework\nand in the specific example, suggested by Chiao, Kozhekin, and Kurizki [Phys.\nRev. Lett., vol. 77, 1254 (1996)], of off-resonant, short-pulse propagation in\nan optical amplifier. We derive in the case of the amplifier a signal-to-noise\nratio that is consistent with the general ARS conclusions when we impose their\ncriteria for distinguishing between superluminal propagation and propagation at\nthe speed c. However, results consistent with the semiclassical arguments of\nCKK are obtained if weaker criteria are imposed, in which case the signal can\nexceed the noise without being \"exponentially large.\" We show that the quantum\nfluctuations of the field considered by ARS are closely related to\nsuperfluorescence noise. More generally we consider the implications of\nunitarity for superluminal propagation and quantum noise and study, in addition\nto the complete and truncated wavepackets considered by ARS, the residual\nwavepacket formed by their difference. This leads to the conclusion that the\nnoise is mostly luminal and delayed with respect to the superluminal signal. In\nthe limit of a very weak incident signal pulse, the superluminal signal will be\ndominated by the noise part, and the signal-to-noise ratio will therefore be\nvery small.",
"arxiv_id": "quant-ph/0004047",
"authors": [
"Bilha Segev",
"Peter W. Milonni",
"James F. Babb",
"Raymond Y. Chiao"
],
"categories": [
"quant-ph"
],
"doi": "10.1103/PhysRevA.62.022114",
"journal_ref": "Phys. Rev. A 62, 022114 (2000)",
"title": "Quantum Noise and Superluminal Propagation",
"url": "https://arxiv.org/abs/quant-ph/0004047"
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