Photodetection of interference fields in the case of a small number of photons

Seng‐Tiong Ho

Sascha Wallentowitz, A. B. Klimov

A model of photodetection using a Bose-Einstein condensate in an atom-chip-based microtrap is analyzed. Atoms absorb photons from the incident light field, receive part of the photon momentum, and leave the trap potential. Upon counting escaped atoms within predetermined time intervals, the photon statistics of the incident light is mapped onto the atom-count statistics. Whereas traditional photodetection theory treats the emission centers of photoelectrons as distinguishable, here the centers of escaping atoms are condensed and thus indistinguishable atoms. From this, an enhancement of the photon-number resolution as compared to the commonly known counting formula is derived for the case of low saturation.

Luis Grave de Peralta, Daniel Domı́nguez

A. V. Kozlovskiĭ

The scheme of an active interferometer for amplification of small optical signals for their subsequent photodetection is proposed. The scheme provides a considerable amplification of signals by preserving their quantum-statistical properties (ideal amplification) and also can improve these properties under certain conditions. The two-mode squeezed state of light produced upon four-wave mixing, which is used for signal amplification, can be transformed to the non-classical state of the output field squeezed in the number of photons. The scheme is phase-sensitive upon amplification of the input coherent signal. It is shown that in the case of the incoherent input signal with the average number of photons ⟨ n s ⟩∼1, the amplification process introduces no additional quantum noise at signal amplification as large as is wished. A scheme is also proposed for the cascade small-signal amplification (⟨ n s ⟩∼1) in the coherent state producing the amplified signal in the squeezed sub-Poisson state, which can be used for the high-resolution detection of weak and ultraweak optical signals.

A. V. Kozlovskiĭ

Dispersive quantum nondemolition measurement of the number of photons is analyzed in the micromaser scheme. It has been shown that the stationary Fock state of the field in a cavity that is considered as the result of quantum nondemolition measurement is realized only in a particular case for strictly determined parameters of the system, and small variation in one of the parameters of the system results in a qualitative change in the field state. In the general case, the field state is characterized by large fluctuations of the number of photons and the mean number of photons, which are very sensitive to the parameters of the system. It has been shown that the detection of the Ramsey interference pattern is possible only when the sequence of atoms passing through the cavity is highly monokinetic.

B. Hüttner, Y. Ben-Aryeh