The Heisenberg limit for laser coherence

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Author(s)
Baker, TJ
Saadatmand, SN
Berry, DW
Wiseman, HM
Year published
2020
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Quantum optical coherence can be quantified only by accounting for both the particle- and wave-nature of light. For an ideal laser beam1–3, the coherence can be thought of roughly as the number of photons emitted consecutively into the beam with the same phase. This number, C, can be much larger than the number of photons in the laser itself, μ. The limit for an ideal laser was thought to be of order μ2 (refs. 4,5). Here, assuming only that a laser produces a beam with properties close to those of an ideal laser beam and that it has no external sources of coherence, we derive an upper bound on C, which is of order μ4. Moreover, ...
View more >Quantum optical coherence can be quantified only by accounting for both the particle- and wave-nature of light. For an ideal laser beam1–3, the coherence can be thought of roughly as the number of photons emitted consecutively into the beam with the same phase. This number, C, can be much larger than the number of photons in the laser itself, μ. The limit for an ideal laser was thought to be of order μ2 (refs. 4,5). Here, assuming only that a laser produces a beam with properties close to those of an ideal laser beam and that it has no external sources of coherence, we derive an upper bound on C, which is of order μ4. Moreover, using the matrix product states method6, we find a model that achieves this scaling and show that it could, in principle, be realized using circuit quantum electrodynamics7. Thus, C of order μ2 is only a standard quantum limit; the ultimate quantum limit—or Heisenberg limit—is quadratically better.
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View more >Quantum optical coherence can be quantified only by accounting for both the particle- and wave-nature of light. For an ideal laser beam1–3, the coherence can be thought of roughly as the number of photons emitted consecutively into the beam with the same phase. This number, C, can be much larger than the number of photons in the laser itself, μ. The limit for an ideal laser was thought to be of order μ2 (refs. 4,5). Here, assuming only that a laser produces a beam with properties close to those of an ideal laser beam and that it has no external sources of coherence, we derive an upper bound on C, which is of order μ4. Moreover, using the matrix product states method6, we find a model that achieves this scaling and show that it could, in principle, be realized using circuit quantum electrodynamics7. Thus, C of order μ2 is only a standard quantum limit; the ultimate quantum limit—or Heisenberg limit—is quadratically better.
View less >
Journal Title
Nature Physics
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© 2020 Nature Publishing Group. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal website for access to the definitive, published version.
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This publication has been entered as an advanced online version in Griffith Research Online.
Subject
Mathematical sciences
Physical sciences
quant-ph
physics.comp-ph
physics.optics