Effects of entanglement in an ideal optical amplifier

In an ideal linear amplifier, the output signal is linearly related to the input signal with an additive noise that is independent of the input. The decoherence of a quantum-mechanical state as a result of optical amplification is usually assumed to be due to the addition of quantum noise. Here we s...

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Bibliographic Details
Published in:Physics letters. A 2018-04, Vol.382 (13), p.887-893
Main Authors: Franson, J.D., Brewster, R.A.
Format: Article
Language:English
Subjects:
Amplifier
Decoherence
Entanglement
Noise
Quantum
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Summary:In an ideal linear amplifier, the output signal is linearly related to the input signal with an additive noise that is independent of the input. The decoherence of a quantum-mechanical state as a result of optical amplification is usually assumed to be due to the addition of quantum noise. Here we show that entanglement between the input signal and the amplifying medium can produce an exponentially-large amount of decoherence in an ideal optical amplifier even when the gain is arbitrarily close to unity and the added noise is negligible. These effects occur for macroscopic superposition states, where even a small amount of gain can leave a significant amount of which-path information in the environment. Our results show that the usual input/output relation of a linear amplifier does not provide a complete description of the output state when post-selection is used. •We show that there can be an exponentially large amount of decoherence in an ideal optical amplifier even when the added noise is arbitrarily small.
ISSN:0375-9601
1873-2429
DOI:10.1016/j.physleta.2018.01.032