CAREER: Realizing the ultrastrong coupling regime of quantum electrodynamics using high-impedance Josephson superconducting circuits

非技术性的。量子电动力学(QED)是描述光和物质如何相互作用的理论。在自然系统中，这种相互作用的强度是由精细结构常数确定的，这是一个基本的自然常数。精细结构常数远小于1，因此光与物质的相互作用很弱。最近，利用人造原子，如量子点，已经制造出有效精细结构常数由材料性质控制的体系。这开启了令人兴奋的可能性，使精细结构保持不变，与自然界中的情况不同--开启了新的物理学体系有待探索。这个项目试图从超导结中创造出人造原子，在那里精细结构常数可以大于1。这将阐明光-物质相互作用的基本问题。同时，这些电路可以用来形成量子计算的容错量子比特。该项目将为研究生和本科生提供最先进的实验技术方面的培训，如纳米制造、低温测量和超导量子比特的量子控制。该协会还将以电路类比为基础，开发一门新的量子力学新课程，并参与面向公众的外展活动。技术上的。这个项目的目的是在超强耦合区域实现量子电动力学(QED)的实验。超强量子电动力学是指单个原子与有效精细结构常数超过1的真空量子场耦合的情况。我们的方法是将超导量子比特(人造原子)耦合到非常高阻抗的微波(场)上，阻抗接近电阻量子的值。如此大的阻抗可以通过在约瑟夫森隧道结阵列或高度无序的超导薄膜中激发微波来实现。谐振器的有效精细结构常数是一种材料特性，因为射频(RF)场的“磁能”主要是由于运动的库珀对的惯性而产生的，而不是由于用磁场对真空施加压力。与超强光-物质相互作用机制相关的新效应，如真空的自发极化、超辐射量子相变和自旋-玻色子物理中的临界行为，将利用强大的超导量子比特技术来探索。

Non-technical. Quantum electrodynamics (QED) is the theory that describes how light and matter interact. In natural systems the strength of this interaction is fixed by the fine structure constant which is a fundamental natural constant. The fine structure constant is much less than one so that light and matter interact only weakly. Recently, using artificial atoms, such as quantum dots, systems have been fabricated where the effective fine structure constant is controlled by the material properties. This opens the exciting possibility of making the fine structure constant different than occurs in nature - opening up new regimes of physics to explore. This project seeks to create artificial atoms out of superconducting junctions where the fine structure constant can be greater than one. This will shed light on fundamental questions of light-matter interaction. At the same time these circuits can be used to form fault tolerant qubits for quantum computing. This project will provide training to graduate and undergraduate students in state-of-the-art experimental techniques such as nanofabrication, low-temperature measurements, and quantum control of superconducting qubits. The PI will also develop a novel new course on quantum mechanics based on an analogy with electrical circuits as well as participating in outreach activities to the general public. Technical. This project aims at an experimental implementation of quantum electrodynamics (QED) in the ultrastrong coupling regime. Ultra-strong QED is a situation where a single atom is coupled to a vacuum quantum field with an effective fine structure constant exceeding a unity. Our approach is to couple superconducting qubits (artificial atoms) to very high-impedance microwaves (fields), with the impedance approaching the value of resistance quantum. Such large impedances can be achieved by exciting microwaves inside either an array of Josephson tunnel junctions or a highly disordered superconducting film. The effective fine structure constant of resonators is a material property, because the "magnetic" energy of the radio-frequency (RF) field is created predominantly due to the inertia of the moving Cooper pairs rather than due to stressing the vacuum with a magnetic field. Novel effects, associated with the ultrastrong light-matter interaction regime, such as spontaneous polarization of vacuum, superradiance quantum phase transitions, and critical behavior in the spin-boson physics, will be explored using the powerful arsenal of superconducting qubit techniques.