Schrödinger's cat beats a quantum limit

Ian Colin Percival

Seung-Woo Lee, Su‐Yong Lee, Jaewan Kim

In this paper, we are interested in detecting the presence of a nearby phase-sensitive object, where traveling light works out under a low-photon loss rate. Here we investigate the optimal quantum phase estimation with generalized multi-component Schrödinger cat states. In addition, we show the optimal conditions of the generalized multi-component cat states for the phase estimation in a lossless scenario. We then demonstrate that the generalized multi-component cat states can beat the performances of the NOON and two-mode squeezed vacuum states in the presence of small loss, while maintaining the quantum advantage over the standard quantum limit, attainable by coherent states. Finally, we propose a generation scheme of the entangled multi-component cat states with current or near-term optical technologies.

Luca Pezzè, Augusto Smerzi

Interferometry with NOON quantum states can provide unbiased phase estimation with a sensitivity scaling as Δθ ∼ 1/ N T given a prior knowledge that the true phase shift θ lies in the interval −π ⩽ θ ⩽ π. The protocol requires a total of N T = 2 p −1 particles (unequally) distributed among p independent measurements and overcomes basic difficulties present in previously proposed approaches. We demonstrate the possibility to obtain a phase sensitivity beating the classical shot-noise limit using published probabilities retrieved experimentally for the creation of Schrödinger cat quantum states containing up to N = 6 beryllium ions.

James D. Stein

Peter John Bussey

Arash Tirandaz, Hamid Reza Naeij, Afshin Shafiee

Abstract In this study, we have proposed a method based on non-equilibrium effects to generate the superposition of macroscopically distinguishable quantum states, known as Schrödinger cat states, by using a Mach–Zehnder interferometry type experiment. The interaction of the input number state with a Kerr medium in the presence of a couple of heat baths in different temperatures in the interaction picture and without imposing a Markov assumption is considered. We have shown that the study of dynamics of the cat states under non-equilibrium condition opens up a way for the robustness of quantum features against the destructive role of the environment, even at high temperature limits. It is verified that the mutual influence of the environments, far from equilibrium, on the open system, makes it possible to revive quantum beats for longer time intervals. Moreover, we have probed how the traits of the environment, like its temperature and the Ohmic, super-Ohmic or sub-Ohmic functionality of the spectral density, may affect the pattern of the oscillation between alive or dead states of the cat.