Universal Thermometry for Quantum Simulation

In situ thermometry of a cold Fermi gas via dephasing impurities

The precise measurement of low temperatures is a challenging, important and fundamental task for quantum science. In particular, in-situ thermometry is highly desirable for cold atomic systems due to their potential for quantum simulation. Here we demonstrate that the temperature of a non-interacting Fermi gas can be accurately inferred from the non-equilibrium dynamics of impurities immersed within it, using an interferometric protocol and established experimental methods. Adopting tools from the theory of quantum parameter estimation, we show that our proposed scheme achieves optimal precisi…

谐振阱中幺正费米气体普适性质的从头算模拟

Ab initio simulation of the universal properties of unitary Fermi gas in a harmonic trap

本研究采用虚拟全同粒子法克服费米子符号问题，对最多100个谐振阱幺正费米子开展从头算模拟，验证了Chang和Bertsch提出的基态能量公式的普适有效性，证明该方法可用于超冷费米气体研究。

Suppression of the critical temperature for superfluidity near the Mott transition: validating a quantum simulator

Ultracold atomic gases in optical lattices have proven to be a controllable, tunable and clean implementation of strongly interacting quantum many-body systems. An essential prospect for such quantum simulators is their ability to map out the phase diagram of fundamental many-body model Hamiltonians. However, the results need to be validated first for representative benchmark problems via state-of-the-art numerical methods of quantum many-body theory. Here we present the first ab-initio comparison between experiments and quantum Monte Carlo simulations for strongly interacting Bose gases on a …

一维Lieb-Liniger气体中Tan接触量的直接测量

Direct measurement of Tan's contact in a one-dimensional Lieb-Liniger gas

本研究针对玻色气体中Tan接触量直接测量受相互作用干扰的问题，采用两阶段膨胀方案实现了一维强关联Lieb-Liniger气体中该量的首次直接测量，结果与理论预测及普适标度律吻合，为相关量子气体研究提供了新途径。

Universal Cooling Scheme for Quantum Simulation

At present, there is a worldwide effort to use cold atoms to simulate strongly correlated quantum many-body systems. It is hoped that these "simulations" will provide solutions to many unsolved problems. However, the relevant energy scales in most of these experiments are so small that one has to go to entropy regimes far below those achievable today. Here, we present a general scheme to extract entropy directly from the region of interest. The late stage of this process is equivalent to a continuous "evaporation", and is able to combat intrinsic heating of the system. For illustration, we sho…

A Single Atom Thermometer for Ultracold Gases

We use single or few Cs atoms as thermometer for an ultracold, thermal Rb cloud. Observing the thermometer atoms' thermalization with the cold gas using spatially resolved fluorescence detection, we find an interesting situation, where a fraction of thermometer atoms thermalizes with the cloud while the other fraction remains unaffected. We compare release-recapture measurements of the thermometer atoms to Monte-Carlo simulations while correcting for the non-thermalized fraction, and recover the cold cloud's temperature. The temperatures obtained are verified by independent time-of-flight meas…

Probing Phases and Quantum Criticality using Deviations from the Local Fluctuation-Dissipation Theorem

Introduction Cold atomic gases in optical lattices are emerging as excellent laboratories for testing models of strongly interacting particles in condensed matter physics. Currently, one of the major open questions is how to obtain the finite temperature phase diagram of a given quantum Hamiltonian directly from experiments. Previous work in this direction required quantum Monte Carlo simulations to directly model the experimental situation in order to extract quantitative information, clearly defeating the purpose of an optical lattice emulator. Here we propose a new method that utilizes devi…

Experimental apparatus for overlapping a ground-state cooled ion with ultracold atoms

Experimental realizations of charged ions and neutral atoms in overlapping traps are gaining increasing interest due to their wide research application ranging from chemistry at the quantum level to quantum simulations of solid-state systems. Here, we describe a system in which we overlap a single ground-state cooled ion trapped in a linear Paul trap with a cloud of ultracold atoms such that both constituents are in the $μ$K regime. Excess micromotion (EMM) currently limits atom-ion interaction energy to the mK energy scale and above. We demonstrate spectroscopy methods and compensation techni…

杨-米尔斯理论量子模拟的通用框架

A universal framework for the quantum simulation of Yang-Mills theory

本文提出基于轨形格点公式的SU(N)杨-米尔斯理论量子模拟通用框架，其截断哈密顿量形式简洁通用，可借助标准量子计算工具实现，还给出了无关理论细节的简易量子电路结构。