Phase-sensitive Linear Amplifier Research Articles

One-atom correlated-emission laser

We study a four-level double-$\ensuremath{\Lambda}$ atomic configuration working as a two photon linear amplifier where two atomic transitions independently interact with cavity mode, while the other transitions are driven by a strong pump field. It is found that our system always works as a phase sensitive linear amplifier with no window for a phase insensitive linear amplifier. We also investigate that the system behaves as a two-photon correlated-emission laser under certain conditions.

Holevo capacity of attenuation channels assisted by linear amplifiers

We derive a capacity formula for attenuation channels assisted by quantum linear amplifiers when the input signal states are restricted to Gaussian states with the same correlation matrix. A phase insensitive linear amplifier and a phase sensitive linear amplifier are compared by using this formula.

Reconstruction of a multimode entangled state using a two-photon phase-sensitive linear amplifier

We propose a model for the measurement of an arbitrary multimode entangled state of the cavity field using two-photon correlated emission laser. We consider two cases: (a) The modes have different frequencies and are detected separately and (b) the modes consist of two orthogonal polarization states and are detected using a single balanced homodyne detector. The basic idea is to amplify the initial multimode state such that there is no-noise in the quadrature of interest and all the noise is fed into the conjugate quadrature component. The amplified noise-free quadrature is prepared in different phases and then corresponding quadrature distribution is measured. The Wigner function of the initial multimode entangled state is then reconstructed by using inverse Radon transformation. This scheme is insensitive to the noise associated with the nonunit efficiency of the detector in the homodyne detection measurement scheme.

Phase-sensitive amplification by the use of degenerate squeezed radiation

We show that a phase-sensitive linear amplifier can be constructed based on pairs of identical two-level atoms, initially in their upper state. Correlations between the atoms are obtained in a high-Q cavity by their interaction with degenerate squeezed radiation. Such correlated pairs of atoms are injected into a linear amplifier, where phase-sensitive amplification is obtained with significant quantum noise reduction.

Quantum-statistical properties of noise in a phase-sensitive linear amplifier.

We present a model for a two-photon phase-sensitive linear amplifier in which the phase sensitivity is introduced by injecting three-level atoms initially prepared in a coherent superposition of upper and lower levels. We have studied the quantum-statistical properties of noise and show that, under certain conditions, the additive noise is in a squeezed vacuum state whose squeezing parameter depends on the atomic variables.

Reduction of quantum fluctuation and suppression of the Gordon–Haus effect with phase-sensitive linear amplifiers

Compared with the use of phase-insensitive linear quantum amplifiers of the same gain G, the use of phase-sensitive linear amplifiers on phase coherent classical light sources in an amplifier-attenuator chain reduces the total quantum noise power by a factor of 4, the homodyne noise variance by 2, and the photon number variance by 2-8 and suppresses the Kerr effect linear phase fluctuation variance as well as the soliton timing-error variance by 2G(2).

A phase sensitive SIS mixer to circumvent the quantum limit

A conventional superconductor-insulator-superconductor (SIS) mixer, that is pumped by a single-frequency local oscillator (LO) functions as a phase-insensitive linear amplifier and may achieve a noise level near the quantum limit of one-half photon added noise per unit bandwidth. A phase-sensitive linear amplifier may have less noise than this quantum limit. To overcome the quantum noise limit with an SIS mixer, a two-LO technique which makes the mixer's gain dependent upon the phase of the incoming signal was used. The phase sensitive gain of this two-LO mixer is experimentally demonstrated. The gain variation from maximum to minimum is more than 20 dB. Theoretical predictions of the noise of the two-LO mixer are presented.

Parametric amplification and signal-to-noise ration in optical transmission lines

The equivalence between squeezing of the loss and phase-dependent amplification of the signal in an optical transmission line is shown. The properties of the radiation at the end of a lossy line, where N phase sensitive linear amplifiers have been inserted, are analyzed and discussed. In the large N limit a logarithmic dependence of the noise on the loss, which reduces the degradation of the signal-to-noise ratio, is obtained. It is also shown that by considering a χ (2) waveguide the same result can be achieved.

Photon-number fluctuations in phase-sensitive linear amplifiers.

It has long been known that amplification will degrade an optical signal and will rapidly destroy any intrinsically quantum features that may have been associated with the input. However, devices that exhibit squeezed fluctuations in the gain or loss medium can reduce the detrimental effects of the inevitable amplifier noise. This makes it possible to retain nonclassical features (in particular squeezing) at higher levels of gain than is possible in conventional devices. In this paper we study the effect of these amplifiers on the photon-number fluctuations. We find that, for suitable inputs, phase-sensitive amplifiers can reduce the tendency for the photon-number distribution to spread and allow us to retain sub-Poissonian statistics at a higher level of gain than is possible in conventional devices.

Phase sensitive heterodyne receivers with SIS quasiparticle mixers

It is noted that it is possible to operate a mixer as a phase-sensitive linear amplifier by pumping with two local oscillators (LOs) separated in frequency by twice the IF (intermediate frequency) and symmetrically located about the signal frequency. In principle a phase-sensitive amplifier can detect a signal without adding any noise. The authors present a formalism developed to describe two-LO mixers, and extend the quantum mixer theory to calculate expressions for the gain and noise of a two-LO mixer. The full quantum mechanical formulation used here enables an analysis of the mixer noise for general input states, for example, a squeezed state. It is demonstrated that a two-LO mixer is phase-sensitive. The results are pertinent to the design of phase-sensitive heterodyne receivers with SIS (superconductor-insulator-superconductor) quasiparticle mixers. >

Quantum limits on noise in linear amplifiers

How much noise does quantum mechanics require a linear amplifier to add to a signal it processes? An analysis of narrow-band amplifiers (single-mode input and output) yields a fundamental theorem for phase-insensitive linear amplifiers; it requires such an amplifier, in the limit of high gain, to add noise which, referred to the input, is at least as large as the half-quantum of zero-point fluctuations. For phase-sensitive linear amplifiers, which can respond differently to the two quadrature phases ($cos\ensuremath{\omega}t$ and $sin\ensuremath{\omega}t$), the single-mode analysis yields an amplifier uncertainty principle---a lower limit on the product of the noises added to the two phases. A multimode treatment of linear amplifiers generalizes the single-mode analysis to amplifiers with nonzero bandwidth. The results for phase-insensitive amplifiers remain the same, but for phase-sensitive amplifiers there emerge bandwidth-dependent corrections to the single-mode results. Specifically, there is a bandwidth-dependent lower limit on the noise carried by one quadrature phase of a signal and a corresponding lower limit on the noise a high-gain linear amplifier must add to one quadrature phase. Particular attention is focused on developing a multimode description of signals with unequal noise in the two quadrature phases.