Aligning Superconducting Transition-Edge Sensors by Reflected Wave Intensity Measurement.

It is critical to accurately align a quantum photon detector such as a superconducting transition-edge sensor (TES) to an optical fiber in order to optimize its detection efficiency. Conventionally, such alignment requires advanced infrared imaging equipment or sophisticated microfabrication. We introduce a novel technique based on the simple idea of reflected wave intensity measurement which allows to determine the boundary of the sensor and align it accurately with the fiber.

Realization of exceptional points along a synthetic orbital angular momentum dimension.

Exceptional points (EPs), at which more than one eigenvalue and eigenvector coalesce, are unique spectral features of non-Hermiticity (NH) systems. They exist widely in open systems with complex energy spectra. We experimentally demonstrate the appearance of paired EPs in a periodical-driven degenerate optical cavity along the synthetic orbital angular momentum dimension with a tunable parameter.

Fiber-sensor alignment based on surface microstructures.

Conventional methods have relied on specialized imaging equipment and advanced fabrication process to solve the problem of accurately aligning a microsensor to an optical fiber which is critical for its detection efficiency. To dramatically lower the barrier to high-precision alignment, we present a technique much easier to implement and much lower in cost. By fabricating replicable alignment and proximity structures on the surface of the sensor chip, we can achieve accurate alignment and position the fiber tip very close to the sensor without damaging it.

Topological band structure via twisted photons in a degenerate cavity.

Synthetic dimensions based on particles' internal degrees of freedom, such as frequency, spatial modes and arrival time, have attracted significant attention. They offer ideal large-scale lattices to simulate nontrivial topological phenomena. Exploring more synthetic dimensions is one of the paths toward higher dimensional physics.

Simulating electrical fields in the orbital angular momentum space of light.

We study a system of coupled degenerate cavities with a switchable beam rotator embedded in the optical path of the main cavity. By exploiting the phase shift of the beam rotator dependent on the orbital angular momentum of the optical modes, and modulating the phase imbalance in the auxiliary cavity, it is shown that the system dynamics is equivalent to that of a charged particle in a 1D lattice subject to both static and time-dependent electrical fields. We investigate interesting physics and phenomena such as Bloch oscillations that arise due to the simulated electrical fields, and discuss how they can be used for practical purposes such as storing optical signals in a quantum memory.

Synthetic-lattice enabled all-optical devices based on orbital angular momentum of light.

All-optical photonic devices are crucial for many important photonic technologies and applications, ranging from optical communication to quantum information processing. Conventional design of all-optical devices is based on photon propagation and interference in real space, which may rely on large numbers of optical elements, and the requirement of precise control makes this approach challenging. Here we propose an unconventional route for engineering all-optical devices using the photon's internal degrees of freedom, which form photonic crystals in such synthetic dimensions for photon propagation and interference.

Dynamically Manipulating Topological Physics and Edge Modes in a Single Degenerate Optical Cavity.

We propose a scheme to simulate topological physics within a single degenerate cavity, whose modes are mapped to lattice sites. A crucial ingredient of the scheme is to construct a sharp boundary so that the open boundary condition can be implemented for this effective lattice system. In doing so, the topological properties of the system can manifest themselves on the edge states, which can be probed from the spectrum of an output cavity field.

Cavity-Assisted Single-Mode and Two-Mode Spin-Squeezed States via Phase-Locked Atom-Photon Coupling.

We propose a scheme to realize the two-axis countertwisting spin-squeezing Hamiltonian inside an optical cavity with the aid of phase-locked atom-photon coupling. By careful analysis and extensive simulation, we demonstrate that our scheme is robust against dissipation caused by cavity loss and atomic spontaneous emission, and it can achieve significantly higher squeezing than one-axis twisting. We further show how our idea can be extended to generate two-mode spin-squeezed states in two coupled cavities.

Quantum simulation of 2D topological physics in a 1D array of optical cavities.

Orbital angular momentum of light is a fundamental optical degree of freedom characterized by unlimited number of available angular momentum states. Although this unique property has proved invaluable in diverse recent studies ranging from optical communication to quantum information, it has not been considered useful or even relevant for simulating nontrivial physics problems such as topological phenomena. Contrary to this misconception, we demonstrate the incredible value of orbital angular momentum of light for quantum simulation by showing theoretically how it allows to study a variety of important 2D topological physics in a 1D array of optical cavities.

Nonlinear coupling of nanomechanical resonators to josephson quantum circuits.

We propose a technique to couple the position operator of a nanomechanical resonator to a SQUID device by modulating its magnetic flux bias. By tuning the magnetic field properly, either linear or quadratic couplings can be realized, with a discretely adjustable coupling strength. This provides a way to realize coherent nonlinear effects in a nanomechanical resonator by coupling it to a Josephson quantum circuit.

Quantum computation with untunable couplings.

Most quantum computer realizations require the ability to apply local fields and tune the couplings between qubits, in order to realize single bit and two bit gates which are necessary for universal quantum computation. We present a scheme to remove the necessity of switching the couplings between qubits for two bit gates, which are more costly in many cases. Our strategy is to compute with encoded qubits in and out of carefully designed interaction free subspaces analogous to decoherence free subspaces.