Phase Estimation from Atom Position Measurements

Phase Estimation With Interfering Bose-Condensed Atomic Clouds

We investigate how to estimate from atom-position measurements the relative phase of two Bose-Einstein condensates released from a double-well potential. We demonstrate that the phase estimation sensitivity via the fit of the average density to the interference pattern is fundamentally bounded by shot noise. This bound can be overcome by estimating the phase from the measurement of $\sqrt N$ (or higher) correlation function. The optimal estimation strategy requires the measurement of the $N$-th order correlation function. We also demonstrate that a second estimation method -- based on the dete…

Diffraction-Unlimited Position Measurement of Ultracold Atoms in an Optical Lattice

We consider a method of high-fidelity, spatially resolved position measurement of ultracold atoms in an optical lattice. We show that the atom-number distribution can be nondestructively determined at a spatial resolution beyond the diffraction limit by tracking the progressive evolution of the many-body wavefunction collapse into a Fock state. We predict that the Pauli exclusion principle accelerates the rate of wavefunction collapse of fermions in comparison with bosons. A possible application of our principle of surpassing the diffraction limit to other imaging systems is discussed.

Position-dependent spin-orbit coupling for ultracold atoms

We theoretically explore atomic Bose-Einstein condensates (BECs) subject to position-dependent spin-orbit coupling (SOC). This SOC can be produced by cyclically laser coupling four internal atomic ground (or metastable) states in an environment where the detuning from resonance depends on position. The resulting spin-orbit coupled BEC phase-separates into domains, each of which contain density modulations - stripes - aligned either along the x or y direction. In each domain, the stripe orientation is determined by the sign of the local detuning. When these stripes have mismatched spatial perio…

非共振种间相互作用及其对冷原子位置响应函数的影响

Non-resonant inter-species interaction and its effect on the position response function of cold atoms

本研究通过钾-钠冷原子混合物实验，发现非共振种间相互作用可显著改变冷原子的位置响应函数，并提出了与实验吻合的量子朗之万理论框架。

Universal scaling of Efimov resonance positions in cold atom systems

Recent cold atom experiments report a surprising universal scaling of the first Efimov resonance position a_{-}^1 by the two-body van der Waals length r_{vdW}. The ratio C=-a_{-}^1/r_{vdW}=8.5~9.5 for identical particles appears to be a constant regardless of the atomic spin configuration, the Feshbach resonance employed to tune the scattering length, and even the atomic species, with K-39 being the only exception. This result indicates that the Efimov energy structure is insensitive to the details of the short range potential. We suggest that the universality results from the quantum reflecti…

Estimation of phase diffusion rates in a condensate interferometer using the Gross-Pitaevskii Equation

Atom interferometers using Bose-Einstein condensates are fundamentally limited by a phase diffusion process that arises from atomic interactions. The Gross-Pitaevskii equation is here used to accurately calculate the diffusion rate for a Bragg interferometer. It is seen to agree with a Thomas-Fermi approximation at large atom numbers and a perturbative approximation at low atom numbers. The diffusion times obtained are generally longer than the coherence times observed in experiments to date.