Talk: Dispersive Quantum Interface with Atoms and Nanophotonic Waveguides
- Abstract: Strong coupling between atoms and light is critical for quantum information processing and precise sensing. A nanophotonic waveguide is a promising platform for realizing an atom-light interface that reaches the strong coupling regime. We calculate the dyadic Green’s function and the modified spontaneous emission rates of atoms in presence of a nanowaveguide, which we use to derive the dispersive light response theory using the Heisenberg-Langevin equations. We study QND measurement and spin squeezing using first-principles stochastic master equations. Based on the birefringence effect, we propose a spin squeezing protocol for the spins encoded in the clock transition of cesium-133. We generalize the concept of cooperativity, which is determined by the ratio between the measurement strength and the decoherence rate in the context of the dispersive waveguide interface. By maximizing the cooperativity per atom, we find the optimal choice of quantization axis that defines the clock states. With this, we predict a peak squeezing of 4.7 dB with 2500 atoms trapped along a realistic nanofiber. To enhance the squeezing and for applications in magnetometry, we propose a protocol based on the Faraday effect for a nanofiber and a square waveguide. Counterintuitively, by placing the atoms at an azimuthal position where the guided probe mode has the lowest intensity, we increase the cooperativity. We find 6.3 dB and 13 dB of peak squeezing for the nanofiber and the square waveguide, respectively, with 2500 atoms.
If interested, I can also briefly discuss a preliminary work on the optimal control theory of atoms preloaded in an optical lattice near a nanophotonic waveguide. The controllability of the system relies on the enhanced inhomogeneous interactions due to multiple scattering of photons among atoms and the global control of internal atomic states of the atoms and the lattice geometry using a microwave control field and the guided modes of the waveguide near the atoms. I will discuss our protocol and demonstrate numerical evidences that one may be able to design universal optimal control waveforms to generate arbitrary collective states and unitary evolution operators in a product quantum space of atoms’ internal states and lattice states with a finite size. An immediate application of our protocol is to demonstrate Boson sampling and hence the quantum supremacy using atoms or atom-like particles on an optical lattice.
- 6月25日周一：10:30am 在新光谱楼M1017做学术报告。跟柯敏老师、罗军老师等讨论。
- . Phys. Rev. A 97, 033829 (2018).
- . Phys. Rev. A 93, 023817 (2016).
- . Xiaodong Qi, PhD dissertation, chapter 3 (2018).