Spontaneous emission of matter waves from a tunable open quantum system.

The decay of an excited atom undergoing spontaneous photon emission into the fluctuating quantum-electrodynamic vacuum is an emblematic  example of the dynamics of an open quantum system. Recent experiments have demonstrated that the gapped photon dispersion in periodic structures, which prevents photons in certain frequency ranges from propagating, can give rise to unusual spontaneous-decay behaviour, including the formation of dissipative bound states1-3. So far, these effects have been restricted to the optical domain. Here we demonstrate similar behaviour in a system of artificial emitters, realized using ultracold atoms in an optical lattice, which decay by emitting matter-wave, rather than optical, radiation into free space. By controlling vacuum coupling and the excitation energy, we directly observe exponential and partly reversible non-Markovian dynamics and detect a tunable bound state that contains evanescent matter waves. Our system provides a flexible platform for simulating open-system quantum electrodynamics and for studying dissipative many-body physics with ultracold atoms4-6.

Optical Encoding Model Based on Orbital Angular Momentum Powered by Machine Learning.

Based on orbital angular momentum (OAM) properties of Laguerre-Gaussian beams LG(p,ℓ), a robust optical encoding model for efficient data transmission applications is designed. This paper presents an optical encoding model based on an intensity profile generated by a coherent superposition of two OAM-carrying Laguerre-Gaussian modes and a machine learning detection method. In the encoding process, the intensity profile for data encoding is generated based on the selection of p and ℓ indices, while the decoding process is performed using a support vector machine (SVM) algorithm. Two different decoding models based on an SVM algorithm are tested to verify the robustness of the optical encoding model, finding a BER =10-9 for 10.2 dB of signal-to-noise ratio in one of the SVM models.

In situ magnetometry for experiments with atomic quantum gases.

Precise control of magnetic fields is a frequent challenge encountered in experiments with atomic quantum gases. Here we present a simple method for performing in situ monitoring of magnetic fields that can readily be implemented in any quantum-gas apparatus in which a dedicated field-stabilization approach is not feasible. The method, which works by sampling several Rabi resonances between magnetically field sensitive internal states that are not otherwise used in a given experiment, can be integrated with standard measurement sequences at arbitrary fields. For a condensate of 87Rb atoms, we demonstrate the reconstruction of Gauss-level bias fields with an accuracy of tens of microgauss and with millisecond time resolution. We test the performance of the method using measurements of slow resonant Rabi oscillations on a magnetic-field sensitive transition and give an example for its use in experiments with state-selective optical potentials.