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Optical coherence and teleportation: Why a laser is a clock, not a quantum channel | | Howard M. Wiseman
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19 Mar 2003 | | Journal: | Proceedings of SPIE Vol. 5111 Fluctuations and Noise in Photonics and Quantum Optics, Eds Derek Abbott, Jeffrey H. Shapiro, Yoshihisa Yamamoto (SPIE, Bellingham, WA, 2003), pp 78-91 | | Subject: | quant-ph | | Abstract: | It has been argued [T. Rudolph and B.C. Sanders, Phys. Rev. Lett. {f 87}, 077903 (2001)] that continuous-variable quantum teleportation at optical frequencies has not been achieved because the source used (a laser) was not `truly coherent’. Van Enk, and Fuchs [Phys. Rev. Lett, {f 88}, 027902 (2002)], while arguing against Rudolph and Sanders, also accept that an `absolute phase’ is achievable, even if it has not been achieved yet. I will argue to the contrary that `true coherence’ or `absolute phase’ is always illusory, as the concept of absolute time on a scale beyond direct human experience is meaningless. All we can ever do is to use an agreed time standard. In this context, a laser beam is fundamentally as good a `clock’ as any other. I explain in detail why this claim is true, and defend my argument against various objections. In the process I discuss super-selection rules, quantum channels, and the ultimate limits to the performance of a laser as a clock. For this last topic I use some earlier work by myself [Phys. Rev. A {f 60}, 4083 (1999)] and Berry and myself [Phys. Rev. A {f 65}, 043803 (2002)] to show that a Heisenberg-limited laser with a mean photon number $mu$ can synchronize $M$ independent clocks each with a mean-square error of $sqrt{M}/4mu$ radians$^2$. | | Source: | arXiv, quant-ph/0303116 | | Services: | Forum | Review | PDF | Favorites | |
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