QFarm Quantum Seminar Series

QFarm presents "Synthetic dimensions for photons: realizing nonreciprocity, artificial magnetic fields and the quantum Hall effect" & "Quantum dynamics of a few-photon parametric oscillator"
Wednesday, April 10, 2019 - 12:00pm
Physics/Astrophysics (Varian II) Building, Room 102/103
Avik Dutt (Stanford) & Zhaoyou Wang (Stanford)
Abstract / Description: 

Synthetic dimensions for photons: realizing nonreciprocity, artificial magnetic fields and the quantum Hall effect
Avik Dutt, Stanford University

The dimensionality of a system strongly determines its properties, both in the classical and quantum regime. Recently, a lot of work has focused on using "synthetic dimensions" to probe higher-dimensional phenomena and topological physics on lower-dimensional systems, drastically reducing experimental complexity. These synthetic dimensions correspond to internal degrees of freedom of ultracold atoms or photons, such as the spin or orbital angular momentum. In this talk, I will discuss our work on realizing synthetic dimensions for photons – specifically using the frequency degree of freedom – in a photonic cavity. I will describe a technique we introduced which enables us to experimentally read-out the band structure of a system in this synthetic space. Next, we extend this technique to perform band structure spectroscopy of a system with multiple synthetic dimensions within a single cavity. This allows the observation of synthetic magnetic fields even for neutral particles like photons, thus breaking reciprocity and time-reversal symmetry. Finally, using this simple structure consisting of a single photonic cavity, we demonstrate how chiral one-way edge states – the hallmark of topological physics and the quantum Hall effect – can be seen directly in the measured band structure.

Quantum dynamics of a few-photon parametric oscillator
Zhaoyou Wang, Stanford University

Modulating the frequency of a harmonic oscillator at nearly twice its natural frequency leads to amplification and self-oscillation. Above the oscillation threshold, the field settles into a coherent oscillating state with a well-defined phase of either 0 or π. We demonstrate a quantum parametric oscillator operating at microwave frequencies and drive it into oscillating states containing only a few photons. The small number of photons present in the system and the coherent nature of the nonlinearity prevents the environment from learning the randomly chosen phase of the oscillator. This allows the system to oscillate briefly in a quantum superposition of both phases at once - effectively generating a nonclassical Schrödinger's cat state. We characterize the dynamics and states of the system by analyzing the output field emitted by the oscillator and implementing quantum state tomography suited for nonlinear resonators. By demonstrating a quantum parametric oscillator and the requisite techniques for characterizing its quantum state, we set the groundwork for new schemes of quantum and classical information processing and extend the reach of these ubiquitous devices deep into the quantum regime.