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arXiv:quant-ph/0212028 · Physical Review A

Reply I to “Comment on ‘Some implications of the quantum nature of laser fields for quantum computations’ ”

S. J. van Enk, Harry J. Kimble

Published Oct 14, 2003• 12 citations
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Abstract

We show that Itano's arguments confirm our conclusion, that entanglement of the atom with the laser field contributes a small but nonzero amount to the total decoherence of an atom in a laser field. This small effect scales as $1/\mathrm{n\ifmmode \bar{}\else \={}\fi{}}$ with $\mathrm{n\ifmmode \bar{}\else \={}\fi{}}$ the average number of photons in the laser pulse.

DOI
10.1103/physreva.68.046302

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Reply II to “Comment on ‘Some implications of the quantum nature of laser fields for quantum computations’ ”

Julio R. Gea-Banacloche

I show that there is no contradiction between the results in my original paper [Phys. Rev. A 65, 022308 (2002)] and Itano's claims in the previous Comment. The error probabilities I calculated from quantum field fluctuations can equivalently be obtained by considering the probability of spontaneous emission by the atom into the field modes that make up the laser pulse.

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Comment on “Some implications of the quantum nature of laser fields for quantum computations”

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A recent discussion of quantum limitations to the fidelity with which superpositions of internal atomic energy levels can be generated by an applied, quantized, laser pulse, is shown to be based on unrealistic physical assumptions. This discussion assumed the validity of Jaynes-Cummings dynamics for an atom interacting with a laser field in free space, that is, when the atom is not surrounded by a resonant cavity. If the laser field is a multimode quantum coherent state, and the Rabi frequency is much greater than the spontaneous decay rate, then the total atomic decoherence rate is on the order of the spontaneous decay rate. With the use of a unitary transformation of the field states due to Mollow, it can be shown that the atomic decoherence rate is the same as if the laser field were treated classically, without any additional contribution due to the quantum nature of the laser field.

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Reply to "Testing the reality of the quantum state"

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Decoherence of a two-state atom driven by coherent light

Hyunchul Nha, H. J. Carmichael

Recent studies of the decoherence induced by the quantum nature of the laser field driving a two-state atom [J. Gea-Banacloche, Phys. Rev. A 65, 022308 (2002); S. J. van Enk and H. J. Kimble, Quantum Inf. Comput. 2, 1 (2002)] have been questioned by Itano [W. M. Itano, Phys. Rev. A 68, 046301 (2003)] and the proposal made that all decoherence is due to spontaneous emission. We analyze the problem within the formalism of cascaded open quantum systems. Our conclusions agree with the Itano proposal. We show that the decoherence, nevertheless, may be divided into two parts---that due to forwards scattering and to scattering out of the laser mode. Previous authors attribute the former to the quantum nature of the laser field.

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Reply to "Comment on ‘Association between quantum paradoxes based on weak values and a realistic interpretation of quantum measurements’"

Anonymous

Physical Review A•May 12, 2025•0 citations
We show that Itano's arguments confirm our conclusion, that entanglement of the atom with the laser field contributes a small but nonzero amount to the total decoherence of an atom in a laser field. This small effect scales as 1/n\ifmmodeˉ\elseˉ\fi1/\mathrm{n\ifmmode \bar{}\else \={}\fi{}}1/n\ifmmodeˉ\elseˉ\fi with n\ifmmodeˉ\elseˉ\fi\mathrm{n\ifmmode \bar{}\else \={}\fi{}}n\ifmmodeˉ\elseˉ\fi the average number of photons in the laser pulse.
A recent discussion of quantum limitations to the fidelity with which superpositions of internal atomic energy levels can be generated by an applied, quantized, laser pulse, is shown to be based on unrealistic physical assumptions. This discussion assumed the validity of Jaynes-Cummings dynamics for an atom interacting with a laser field in free space, that is, when the atom is not surrounded by a resonant cavity. If the laser field is a multimode quantum coherent state, and the Rabi frequency is much greater than the spontaneous decay rate, then the total atomic decoherence rate is on the order of the spontaneous decay rate. With the use of a unitary transformation of the field states due to Mollow, it can be shown that the atomic decoherence rate is the same as if the laser field were treated classically, without any additional contribution due to the quantum nature of the laser field.
Recent studies of the decoherence induced by the quantum nature of the laser field driving a two-state atom [J. Gea-Banacloche, Phys. Rev. A 65, 022308 (2002); S. J. van Enk and H. J. Kimble, Quantum Inf. Comput. 2, 1 (2002)] have been questioned by Itano [W. M. Itano, Phys. Rev. A 68, 046301 (2003)] and the proposal made that all decoherence is due to spontaneous emission. We analyze the problem within the formalism of cascaded open quantum systems. Our conclusions agree with the Itano proposal. We show that the decoherence, nevertheless, may be divided into two parts---that due to forwards scattering and to scattering out of the laser mode. Previous authors attribute the former to the quantum nature of the laser field.