Presence Of Phase Diffusion Research Articles

A robust hybrid receiver for binary phase-shift keying discrimination in the presence of phase noise

We address the problem of coherent state discrimination in the presence of phase diffusion. We investigate the role of the HYbrid Near-Optimum Receiver (HYNORE) we proposed in [J. Opt. Soc. Am. B 40 (2023) 705] in the task of mitigating the noise impact. We prove the HYNORE to be a robust receiver, outperforming the Displacement Photon-Number-Resolving (DPNR) receiver and beating the standard quantum limit in particular regimes. We introduce the maximum tolerable phase noise [Formula: see text]max as a figure of merit for the receiver robustness and show that HYNORE increases its value with respect to the DPNR receiver.

Effects of finite bandwidth on atomic grating in a three level ladder type system

In this paper, we study the atomic grating produced by a three-level ladder type system which interacts with a strong standing microwave drive field of finite bandwidth. The upper levels of the atoms are coupled by the drive field while the probe field is applied on the lower two levels. We find that in the presence of phase fluctuations associated with the microwave drive field, the diffraction intensities are significantly affected. Our results show that if the probe and microwave drive are on resonance with their respective atomic transitions, then the diffraction intensities can be improved by properly adjusting the strength of the drive field. However, if the probe field is detuned from the resonance, then the diffraction intensities can be improved by appropriately selecting the strength of the drive field, probe detuning and interaction length of the medium. Interestingly, our results also show that the effects of phase grating can also be enhanced by a pertinent choice of various parameters even in the presence of phase diffusion. This results in the suppression of the zeroth order intensity while the first order intensity is increased.

Quantum phase communication channels assisted by non-deterministic noiseless amplifiers

We address quantum $M$-ary phase-shift keyed (PSK) communication channels in the presence of phase diffusion, and analyze the use of probabilistic noiseless linear amplifiers (NLA) to enhance performance of coherent signals. We consider both static and dynamical phase diffusion and assess the performances of the channel for ideal and realistic phase receivers. Our results show that NLA employed at the stage of signal preparations is a useful resource, especially in the regime of weak signals. We also discuss the interplay between the use of NLA, and the memory effects occurring with dynamical noise, in determining the capacity of the channel.

Phase estimation for an SU(1,1) interferometer in the presence of phase diffusion and photon losses

We theoretically study the quantum Fisher information (QFI) of the SU(1,1) interferometer with phase shifts in two arms taking account of realistic noise effects. A generalized phase transform including the phase diffusion effect is presented by the purification process. Based on this transform, the analytical QFI and the bound to the quantum precision are derived when considering the effects of phase diffusion and photon losses simultaneously. To beat the standard quantum limit with the reduced precision of phase estimation due to noisy, the upper bounds of decoherence coefficients as a function of total mean photon number are given.

Squeezing-enhanced phase-shift-keyed binary communication in noisy channels

We address binary phase-shift-keyed communication channels based on Gaussian states and prove that squeezing improves state discrimination at fixed energy of the channel, also in the presence of phase diffusion. We then assess performances of homodyne detection against the ultimate quantum limits to discrimination, and show that homodyning achieves optimality in large noise regime. Finally, we consider noise in the preparation of the seed signal (before phase encoding) and show that also in this case squeezing may improve state discrimination in realistic conditions.

Weak measurements and the joint estimation of phase and phase diffusion

Weak measurements offer the possibility of tuning the information acquired on a system, hence the imposed disturbance. This suggests that it could be a useful tool for multi-parameter estimation, when two parameters can not be measured simultaneously at the quantum limit. Here we discuss their use for phase estimation in the presence of phase diffusion in the context of polarimetry, a scenario which is conveniently cast in terms of a two-level quantum system in many relevant cases.

Noisy quantum phase communication channels

We address quantum phase channels, i.e communication schemes where information is encoded in the phase-shift imposed to a given signal, and analyze their performances in the presence of phase diffusion. We evaluate mutual information for coherent and phase-coherent signals, and for both ideal and realistic phase receivers. We show that coherent signals offer better performances than phase-coherent ones, and that realistic phase channels are effective ones in the relevant regime of low energy and large alphabets.

Quantum interferometry with binary-outcome measurements in the presence of phase diffusion

Optimal measurement scheme with an efficient data processing is important in quantum-enhanced interferometry. Here we prove that for a general binary outcome measurement, the simplest data processing based on inverting the average signal can saturate the Cram\'{e}r-Rao bound. This idea is illustrated by binary outcome homodyne detection, even-odd photon counting (i.e., parity detection), and zero-nonzero photon counting that have achieved super-resolved interferometric fringe and shot-noise limited sensitivity in coherent-light Mach-Zehnder interferometer. The roles of phase diffusion are investigated in these binary outcome measurements. We find that the diffusion degrades the fringe resolution and the achievable phase sensitivity. Our analytical results confirm that the zero-nonzero counting can produce a slightly better sensitivity than that of the parity detection, as demonstrated in a recent experiment.

Homodyne detection as a near-optimum receiver for phase-shift-keyed binary communication in the presence of phase diffusion

We address binary optical communication channels based on phase-shift keyed coherent signals in the presence of phase diffusion. We prove theoretically and demonstrate experimentally that a discrimination strategy based on homodyne detection is robust against this kind of noise for any value of the channel energy. Moreover, we find that homodyne receiver beats the performance of Kennedy receiver as the signal energy increases, and achieves the Helstrom bound in the limit of large noise.

Optical Phase Estimation in the Presence of Phase Diffusion

The measurement problem for the optical phase has been traditionally attacked for noiseless schemes or in the presence of amplitude or detection noise. Here we address the estimation of phase in the presence of phase diffusion and evaluate the ultimate quantum limits to precision for phase-shifted Gaussian states. We look for the optimal detection scheme and derive approximate scaling laws for the quantum Fisher information and the optimal squeezing fraction in terms of the total energy and the amount of noise. We also find that homodyne detection is a nearly optimal detection scheme in the limit of very small and large noise.

Optimal Gaussian squeezed states for atom interferometry in the presence of phase diffusion

We optimize the signal-to-noise ratio of a Mach-Zehnder atom interferometer with Gaussian squeezed input states, in the presence interactions. For weak interactions, our results coincide with Phys. Rev. Lett. {\bf 100}, 250406 (2008), with optimal initial number-variance $\sigma_o\propto N^{1/3}$ and optimal signal-to-noise ratio $s_o\propto N^{2/3}$ for total atom number $N$. As the interaction strength $u$ increases past unity, phase-diffusion becomes dominant, leading to a transition in the optimal squeezing from initial number-squeezing to initial {\it phase}-squeezing with $\sigma_o\propto\sqrt{uN}$ and $s_o\propto\sqrt{N/u}$ shot-noise scaling. The initial phase-squeezing translates into hold-time number-squeezing, which is less sensitive to interactions than coherent states and improves $s_o$ by a factor of $\sqrt{u}$.

Phase estimation in the presence of phase diffusion: the qubit case

In this paper we address the estimation of the phase shift imposed on a qubit in the presence of phase diffusion. We evaluate the ultimate quantum limits to precision and determine optimal probes and measurements achieving those bounds. We also analyse in detail the performances of spin measurements and have found that although the corresponding Fisher information depends on the unknown value of the phase shift, we may still achieve the ultimate bound using a two-step adaptive method.

Experimental estimation of one-parameter qubit gates in the presence of phase diffusion

We address estimation of one-parameter qubit gates in the presence of phase diffusion. We evaluate the ultimate quantum limits to precision, seek for optimal probes and measurements, and demonstrate an optimal estimation scheme for polarization qubits. An adaptive method to achieve optimal estimation in any working regime is also analyzed in details and experimentally implemented.

Correlations in nondegenerate parametric oscillation: Squeezing in the presence of phase diffusion.

We present a quantum theory of the nondegenerate parametric oscillator above threshold. The effect of signal and idler phase diffusion on the various types of external squeezing spectral measurements is discussed.