dorsal/arxiv
View SchemaDefending Continuous Variable Teleportation: Why a laser is a clock, not a quantum channel
| Authors | Howard M. Wiseman |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/0403137 |
| URL | https://arxiv.org/abs/quant-ph/0403137 |
| DOI | 10.1088/1464-4266/6/8/035 |
| Journal | Journal of Optics B, S849-S859, 2004 |
Abstract
It has been argued [T. Rudolph and B.C. Sanders, Phys. Rev. Lett. {\bf 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, {\bf 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 (at least for frequencies 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 {\bf 60}, 4083 (1999)] and Berry and myself [Phys. Rev. A {\bf 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 $\sqrt{M}/4\mu$ radians$^2$.
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"abstract": "It has been argued [T. Rudolph and B.C. Sanders, Phys. Rev. Lett. {\\bf 87},\n077903 (2001)] that continuous-variable quantum teleportation at optical\nfrequencies has not been achieved because the source used (a laser) was not\n`truly coherent\u0027. Van Enk, and Fuchs [Phys. Rev. Lett, {\\bf 88}, 027902\n(2002)], while arguing against Rudolph and Sanders, also accept that an\n`absolute phase\u0027 is achievable, even if it has not been achieved yet. I will\nargue to the contrary that `true coherence\u0027 or `absolute phase\u0027 is always\nillusory, as the concept of absolute time (at least for frequencies beyond\ndirect human experience) is meaningless. All we can ever do is to use an agreed\ntime standard. In this context, a laser beam is fundamentally as good a `clock\u0027\nas any other. I explain in detail why this claim is true, and defend my\nargument against various objections. In the process I discuss super-selection\nrules, quantum channels, and the ultimate limits to the performance of a laser\nas a clock. For this last topic I use some earlier work by myself [Phys. Rev. A\n{\\bf 60}, 4083 (1999)] and Berry and myself [Phys. Rev. A {\\bf 65}, 043803\n(2002)] to show that a Heisenberg-limited laser with a mean photon number $\\mu$\ncan synchronize $M$ independent clocks each with a mean-square error of\n$\\sqrt{M}/4\\mu$ radians$^2$.",
"arxiv_id": "quant-ph/0403137",
"authors": [
"Howard M. Wiseman"
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"doi": "10.1088/1464-4266/6/8/035",
"journal_ref": "Journal of Optics B, S849-S859, 2004",
"title": "Defending Continuous Variable Teleportation: Why a laser is a clock, not a quantum channel",
"url": "https://arxiv.org/abs/quant-ph/0403137"
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