Preserving quantum resources in dissipative environments is a fundamental challenge in quantum information processing. While environmental interactions usually degrade quantum resources, we theoretically show that in a Quantum Brownian Motion (QBM) channel, continuous-variable state discrimination can be improved by increasing, rather than minimizing, the initial thermal noise. Specifically, without suppressing the inherent environmental dissipation, when combined with squeezing, this initial noise induces a coherence preservation mechanism driven by the transient non-thermalization of the probe with the bath. This preservation translates into a pronounced reduction in error probabilities for state discrimination between orthogonal squeezing directions. Furthermore, we also show that quadrature homodyne detection achieves near-optimal performance, approaching the Helstrom limit. These results highlight the advantage of exploiting thermal-squeezed states, offering a robust physical architecture for quantum communication in high-temperature environments.
Preserving quantum resources in dissipative environments is a fundamental challenge in quantum information processing. While environmental interactions usually degrade quantum resources, we theoretically show that in a Quantum Brownian Motion (QBM) channel, continuous-variable state discrimination can be improved by increasing, rather than minimizing, the initial thermal noise. Specifically, without suppressing the inherent environmental dissipation, when combined with squeezing, this initial noise induces a coherence preservation mechanism driven by the transient non-thermalization of the probe with the bath. This preservation translates into a pronounced reduction in error probabilities for state discrimination between orthogonal squeezing directions. Furthermore, we also show that quadrature homodyne detection achieves near-optimal performance, approaching the Helstrom limit. These results highlight the advantage of exploiting thermal-squeezed states, offering a robust physical architecture for quantum communication in high-temperature environments.
Pulse position modulation (PPM) is widely adopted in free space optical transmission, and is a candidate for deep space transmission, also in quantum form. The change of signal photon number probability distribution is caused by thermal noise in quantum PPM format. We prove that squeezing improves state discrimination at fixed channel energy, and also in the presence of thermal noise. Then we compare the difference between coherent state and squeezed state in thermal noise and reveal that the squeezed state has better robustness. It is shown that for the fixed channel energy, the larger the squeezed parameter is not the better. For some given total channel energies, we further study and get the optimal squeezed parameter. Finally, combined with the actual situation, the simulation results show that, as a resource for noisy quantum communication channels, the squeezing operation can improve the quality of deep space quantum communication system with PPM.
Quantum metrology promises precision beyond classical limits, yet environmental noise typically degrades the quantum resources required for such enhancement. In this work, we investigate frequency estimation in noisy continuous-variable systems, focusing on two complementary strategies to mitigate decoherence: Hamiltonian engineering and the exploitation of non-Markovian dynamics. By embedding squeezing directly into the system Hamiltonian, we show that the quantum Fisher information (QFI) may acquire a tunable higher-order time dependence, leading to enhanced sensitivity in the short-time regime. Moving beyond the Markovian approximation, we employ the quantum Brownian motion model to demonstrate that structured environments with finite memory can induce information backflow, temporarily restoring and even improving estimation precision relative to the unitary limit. We further assess the achievability of these bounds via Gaussian measurements, identifying regimes where homodyne, heterodyne, and optimized general-dyne measurements saturate the QFI, and noting that stronger squeezing widens the gap, potentially requiring non-Gaussian measurement strategies. Our results establish that jointly tailoring system Hamiltonian and environmental memory offers a viable route toward robust quantum-enhanced frequency estimation in open systems.
Quantum state discrimination plays a central role in quantum information and communication. For the discrimination of optical quantum states, the two most widely adopted measurement techniques are photon detection, which produces discrete outcomes, and homodyne detection, which produces continuous outcomes. While various protocols using photon detection have been proposed for optimal and near-optimal discrimination between two coherent states, homodyne detection is known to have higher error rates, with its minimum achievable error rate often referred to as the Gaussian limit. In this work, we demonstrate that, despite the fundamental differences between discretely labelled and continuously labelled measurements, continuously labelled non-Gaussian measurements can also achieve near-optimal coherent state discrimination. We design two discrimination protocols that surpass the Gaussian limit: one using non-Gaussian unitary operations with homodyne detection, and another based on orthogonal polynomials. Our results show that photon detection is not required for near-optimal coherent state discrimination and that we can achieve error rates close to the Helstrom bound at low energies with continuously labelled measurements. We also find that our schemes maintain an advantage over the photon detection-based Kennedy receiver for a moderate range of coherent state amplitudes.
In this paper, we investigate secure quantum teleportation (SQT) of squeezed coherent states in the presence of a noisy Gaussian environment. Unlike most previous studies that consider coherent states as the input to be teleported, we take squeezed coherent states as the information carriers and analyze how the squeezing of the input state influences the performance and security of the teleportation protocol. The quantum channel is modeled by a two-mode squeezed vacuum state shared between Alice and Bob, which interacts with a common squeezed thermal reservoir. The security of teleportation is ensured by simultaneously satisfying two conditions: a teleportation fidelity exceeding the classical limit [Formula: see text] and the existence of two-way quantum steering of the resource state. Using the covariance matrix formalism and the Lindblad master equation for open quantum systems, we study the time evolution of teleportation fidelity and Gaussian steering under the combined effects of dissipation, temperature and environmental squeezing. The results show that the squeezing of the input coherent state plays a significant role in modifying the robustness of secure quantum teleportation against environmental noise. In particular, for suitable parameter regimes, input-state squeezing can enhance the tolerance of the protocol to thermal fluctuations and de-coherence, extending the temporal range in which SQT is achievable. These findings highlight the importance of the choice of input states in continuous-variable quantum communication protocols and provide new insights for optimizing secure quantum teleportation in realistic noisy environments.
Optical loss is a common bottleneck in photonic quantum information processing, undermining the quantum advantage over classical approaches. Although several countermeasures, such as quantum distillation and error correction, have been proposed, they typically require experimentally demanding non-Gaussian operations. Here, we demonstrate a Gaussian-only scheme that suppresses loss-induced decoherence for general, unknown optical quantum states. By injecting a squeezed vacuum state into an environment of the loss channel and performing feedforward based on environmental monitoring, the scheme effectively suppresses loss-induced noise. Our programmable loop-based optical circuit allows us to implement the scheme for several types of loss-sensitive non-Gaussian states under various loss conditions for up to five steps, and directly compare the results with the unsuppressed case. Our results show that the scheme consistently mitigates state degradation, preserving higher fidelity and Wigner negativity than without suppression. This approach can be applied to mitigating a broad class of errors in optical systems and extending quantum memory lifetimes. Moreover, it is compatible with other loss-suppression techniques and extendable to physical platforms beyond optics, offering a promising route toward reducing the overhead required for fault-tolerant quantum information processing.
Gaussian quantum channels are relevant operations in continuous variable systems. In general, given an arbitrary state, the action on it is well known, provided that the quantum channels are completely characterized. In this work, we have studied the role played by quantum coherence in the estimation of Gaussian channel parameters. For this purpose, we start by considering an initial single-mode vacuum state where coherence is generated through displaced or/and squeezing operations. Then, we consider a probe state with two resources, the average thermal number and the quantum coherence. The results are computed using the quantum Fisher information (QFI) as well as some gain functions defined in the work. We applied the estimation protocol for two paradigmatic bosonic Gaussian channels: the thermal attenuator and the thermal amplifier. Our results show that for the vacuum initial state, coherence can be exploited to obtain a high QFI. Moreover, we can state two important facts: the first being that for a small parameter region of a channel, the QFI depends on the mechanism used to generate the coherence, while the second is that the QFI depends not only on the amount of coherence but also on how it changes as a function of the parameter to be estimated. For the probe state, including also an average thermal number, the two examples show that thermal resources are not always beneficial to the QFI and that this depends on the channel structure. For the attenuator channel, the optimal probe state is only limited by the ability to implement an average thermal number and generate an amount of coherence, while for the amplifier channel, the vacuum probe state with coherence is the optimal state. Finally, we obtain a direct relation between the quantum Fisher information and the relative entropy of coherence, allowing, in principle, an experimental verification based on the measurement of the covariance matrix of the probe system.