arXiv subjects

Mengbo Guo

Publications and source records attributed to Mengbo Guo.

6 recordsLinked to original sources

arXiv2026

Exact Virtual Channel Programming with Vanishing Excess Overhead

A finite-dimensional physical processor cannot exactly program a continuous family of distinct unitary channels. We show that this obstruction becomes quantitative when the target channel is stored in a normalized Choi state and its output observables are reconstructed by sampling physical channels and classically post-processing their measurement outcomes. For arbitrary $d$-dimensional channels, we construct a target-independent exact reconstruction protocol and prove the optimal one-copy sampling overhead, which grows quadratically with system dimension. We further prove the sharp fixed-$d$ law that the excess overhead vanishes inversely with the number of identical Choi programs. The upper bound combines deterministic port-based teleportation with a quasi-decomposition that corrects its depolarizing distortion. The converse maps any low-overhead reconstruction protocol to a physical learner of unknown unitaries and uses local quantum estimation to recover the same leading coefficient. These results recast the universal no-programming obstruction as a quantitative trade-off between quantum program memory and classical sampling, with a leading cost that reflects the locally learnable unitary degrees of freedom.

quant-ph↗

arXiv2025

Programmable Open Quantum Systems

Programmability is a unifying paradigm for enacting families of quantum transformations via fixed processors and program states, with a fundamental role and broad impact in quantum computation and control. While there has been a shift from viewing open systems solely as a source of error to treating them as a computational resource, their programmability remains largely unexplored. In this work, we develop a framework that characterizes and quantifies the programmability of Lindbladian semigroups by combining physically implementable retrieval maps with time varying program states. Within this framework, we identify quantum programmable classes enabled by symmetry and stochastic structure, including covariant semigroups and fully dissipative Pauli Lindbladians with finite program dimension. We further provide a necessary condition for physical programmability that rules out coherent generators and typical dissipators generating amplitude damping. For such nonphysically programmable cases, we construct explicit protocols with finite resources. Finally, we introduce an operational programming cost, defined via the number of samples required to program the Lindbladian, and establish its core structural properties, such as continuity and faithfulness. These results provide a notion of programming cost for Lindbladians, bridge programmable channel theory and open system dynamics, and yield symmetry driven compression schemes and actionable resource estimates for semigroup simulation and control in noisy quantum technologies.

quant-ph↗

arXiv2025

Localization behavior in a Hermitian and non-Hermitian Raman lattice

We propose a flexible Raman lattice system for alkaline-earth-like atoms to theoretically investigate localization behaviors in a quasi-periodic lattice with controllable non-Hermiticity. Our analysis demonstrates that critical phases and mobility edges can arise by adjusting spin-dependence of the incommensurate potentials in the Hermitian regime. With non-Hermiticity introduced by spin-selective atom loss, our calculations reveal that critical localization behaviour in this system can be suppressed by dissipation. Our work provides insights into interplay between quasi-periodicity and non-Hermitian physics, offering a new perspective on localization phenomena.

cond-mat.quant-gas↗

arXiv2024

Third-Order Exceptional Point in Non-Hermitian Spin-Orbit-Coupled cold atoms

Exceptional points (EPs) has seen substantial advances in both experiment and theory. However, in quantum systems, higher-order exceptional points remain of great interest and possess numerous intriguing properties yet to be fully explored. Here, we describe a \emph{PT} symmetry-protected three-level non-Hermitian system with the dissipative spin-orbit-coupled (SOC) fermions in which a third-order exceptional point (EP3) emerges when both the eigenvalues and eigenstates of the system collapse into one. The band structure and its spin dynamics are explored for $^{173}$Yb fermions. We highlight the enhanced sensitivity to the external perturbation of EP3 with cubic-root energy dispersion. Additionally, we investigate the second-order exceptional point (EP2) with square-root energy dispersion in a three-level quantum system with the absence of parity symmetry, which proves that the enhanced sensitivity closely relates to the symmetries of the NH system. Furthermore, we analyze the encircling behavior of EP3 in terms of the adiabatic limit and the nonadiabatic dynamics and discover some different results from that of EP2.

cond-mat.quant-gas↗

arXiv2024

Thermodynamics of Spin-Imbalanced Fermi Gases with SU(N) Symmetric Interaction

Thermodynamics of degenerate Fermi gases has been extensively studied through various aspects such as Pauli blocking effects, collective modes, BCS superfluidity, and more. Despite this, multi-component fermions with imbalanced spin configurations remain largely unexplored, particularly beyond the two-component scenario. In this work, we generalize the thermodynamic study of SU($N$) fermions to spin-imbalanced configurations based on density fluctuations. Theoretically, we provide closed-form expressions of density fluctuation across all temperature ranges for general spin population setups. Experimentally, after calibrating the measurements with deeply degenerate $^{173}$Yb Fermi gases under spin-balanced configurations ($N\leq$~6), we examine the density fluctuations in spin-imbalanced systems. Specifically, we investigate two-species and four-species configurations to validate our theoretical predictions. Our analysis indicates that interaction enhancement effects can be significant even in highly spin-imbalanced systems. Finally, as an application, we use this approach to examine the decoherence process. Our study provides a deeper understanding of the thermodynamic features of spin-imbalanced multi-component Fermi gases and opens new avenues for exploring complex quantum many-body systems.

cond-mat.quant-gas↗

arXiv2022

Novel Sample Stages for Detecting Magnetic Feedback Due to Superconducting Transition Based on the Mirror Image Method

In traditional detection of the magnetic signal in the experiment, complicated electronic devices are usually set up to explore the feedback from the superconducting transition due to the external magnetic field. This kind of direct detection will be more time-consuming, especially in experiments with strict requirements like low temperature and high vacuum. To make the signal detection more convenient to realize, we design a novel sample stage with functions of both placement and acceptance of the magnetic field based on the mirror image method. This device consists of two parts, drive coils and receiver coils. The drive coils apply the initial magnetic field to the superconducting material while the receiver coils are used to collect the magnetic signal feedback. With only the power supply and a signal amplifier needed to be connected to the coils, our device makes it more convenient to finish magnetic signal detection. Another highlight of our design is using first-principles numerical simulation to help accurately determine the size and parameters of the device. With these calculated parameters, we build a 3D model of the device using the software SOLIDWORKS.

cond-mat.supr-con↗