Non-Gaussian states, and specifically the paradigmatic cat state, are well known to be very sensitive to losses. When propagating through damping channels, these states quickly lose their nonclassical features and the associated negative oscillations of their Wigner function. However, by squeezing the superposition states, the decoherence process can be qualitatively changed and substantially slowed down. Here, as a first example, we experimentally observe the reduced decoherence of squeezed optical coherent-state superpositions through a lossy channel. To quantify the robustness of states, we introduce a combination of a decaying value and a rate of decay of the Wigner function negativity. This work, which uses squeezing as an ancillary Gaussian resource, opens new possibilities to protect and manipulate quantum superpositions in phase space.
When individual particles pass through a double slit, a fringe pattern appears on a screen. If an observer detects the path of the particle, the interference fringes disappear. This is called the quantum decoherence. In this paper, we discuss a parameter estimation problem using the quantum decohenrece in the double-slit experiment. As a simple model, we consider a massive scalar field interacting with the particle which have passed through the double slit. The scalar field, as well as the observer, can induce the loss of the fringe pattern of the particle. Because the interference fringes of the particle depend on the field mass and coupling, we can estimate the field parameters from the fringes. For qualitative analysis, we introduce the interferometric visibility of the fringe pattern and the Fisher information (FI) matrix of the field mass and coupling. Using the fringe pattern observed on the distant screen, we derive a simple relation between the visibility and the FI matrix. Also if we focus on FI of the mass, then we find that FI characterizes the wave-particle duality in the double-slit experiment.
Abstract In certain analyses of quantum systems, it is common to disregard the dissipation effect and focus solely on decoherence. This is because decoherence typically occurs on a much shorter timescale compared to dissipation. However, in order to gain insight into the role of dissipation, we examine the interference pattern in a double-slit experiment while considering both effects. To do so, we establish time scales for decoherence and dissipation and acknowledge the possibility of these effects occurring in close proximity. By comparing the relative intensity and fringe visibility between a purely decoherent model and a model that incorporates both decoherence and dissipation, we observe that when the time scales of decoherence and dissipation are similar, there exists a propagation time interval where dissipation contributes to a faster degradation of quantum features compared to the sole influence of decoherence. Hence, it is crucial to consider both decoherence and dissipation effects, especially when their time scales are closely aligned, to gain a comprehensive understanding of quantum behavior.
Wigner negativity has been shown to be a resource in quantum computing, raising the question of how to efficiently produce states with a large Wigner negativity. Cubic Gaussian states, obtained when a cubic gate is applied to a Gaussian state, have been proposed as candidates for this purpose. We show that cubic Gaussian states with a large Wigner negativity
N necessarily have a short decoherence time
τ that is bounded above by
N−2. In other words, a large Wigner negativity comes at a cost: the decoherence time
τ of cubic Gaussian states decreases at least quadratically in the negativity
N. Maximizing
τ at fixed Wigner negativity
N, we show that this upper bound is reached by optimal cubic Gaussian states. They have the property that for large negativity, the optimal squeezing scales as
lnN and the optimal cubicity as
N−1. Optimal cubic Gaussian states with large negativity can therefore be constructed with small cubicity, provided sufficient squeezing is applied. However, their decoherence time decreases with growing negativity. In addition, we show that their preparation is extremely sensitive to thermal noise. Finally, we compare, for each integer
n, the optimal cubic Gaussian state with the
nth Fock state that has the same negativity: despite their pronounced differences in photon number distribution and Wigner function, we show that they have similar, be it slightly larger, decoherence times and entanglement generating potential through a beam splitter.
The elements of reality coined by Einstein, Podolsky, and Rosen promoted a series of fundamental discussions involving the notion of quantum correlations and physical realism. The superposition principle applied in the double-slit experiment with matter waves highlights the need for a critical review of the adoption of physical realism in the quantum realm. In this work, we employ a measure of physical irrealism and consider an initial contractive state in the double-slit setup for which position and momentum variables of a single particle are initially correlated. We investigate how the behavior of the irrealism can help us to obtain information about the interference pattern, wavelike, and particlelike properties in the double-slit setup with matter waves. We find that there is a time of propagation that minimizes the irrealism, and around this point the state at the detection screen is squeezed in position and momentum in comparison with the standard Gaussian superposition. Interestingly, we show that the maximum visibility and the number of interference fringes are related to the minimum of the irrealism. Moreover, we demonstrate a monotonic relation between the irrealism and visibility around the time of minimum. Then, we argue how to use these results to indirectly measure the irrealism for position variable from the fringe visibility.