The research in the group is focussed on two main themes: Quantum (nano)mechanics and Quantum Circuits.

Quantum (nano)mechanics

A core activity in the group is focussed on building and exploring quantum states of nanomechanical resonators. To do this, we used a tool called “optomechanics”. Optomechanics is a technique in which one can use light trapped in a cavity to probe and control the motion of a mechanical resonator at the quantum level.

In the SteeleLab, the main focus of our research is implementing optomechanical systems using mechanical resonators and microwave photons. To do this, we use low-loss superconducting devices operating at millikelvin temperatures that resonate at microwave frequencies and can trap microwave photons for long periods of time. In these superconducting devices, we engineer a coupling of the trapped microwave fields to the motion of a high quality-factor mechanical resonator that oscillates at frequencies in the range of kHz to MHz. Using the coupling of these microwave photons to phonons in the mechanical object, we aim to cool the mechanical resonator to it’s quantum ground state and detect it’s motion with quantum sensitivity by looking at the microwave “light” that comes back out.

To trap the microwave light, we use a wide range of superconducting cavities, ranging from coplanar waveguides and 3D microwave cavities to superconducting resonant devices based on the Josephson effect, such as transmon qubits and SQUID LC resonators. We currently have three main approaches we pursue:

mK Ultracoherent mechanics

Here, we use silicon nitride membranes coupled to superconducting microwave cavities to implement ultracoherent optomechanics at mK temperatures.

Flux-mediated optomechanics

Here, we explore a new optomechanical coupling using quantum interference in a SQUID circuit to couple to mechanical displacements that offers the potential of scaling to new regimes of signal-photon coupling rates

Mechanics and qubits

Here, we are exploring schemes to directly mechanical resonators to qubits by incorporating both into the same device. In our first attempt below, the mechanical element was too weakly coupled, but this did lead to a new direction in our group explore the physics of quantum circuits.

Related publications:

Large cooperativity and microkelvin cooling with a 3D optomechanical cavity
Mingyun Yuan, Vibhor Singh, Yaroslav M. Blanter, Gary A. Steele
Nature Communications 6, 8491 (2015) arxiv

Coupling microwave photons to a mechanical resonator using quantum interference
I. C. Rodrigues, D. Bothner, G. A. Steele

Multi-mode ultra-strong coupling in circuit quantum electrodynamics
Sal J. Bosman, Mario F. Gely, Vibhor Singh, Alessandro Bruno, Daniel Bothner, Gary A. Steele
npj Quantum Information 3, 46 (2017) arxiv

Quantum Circuits

Recently, we have been building a second core activity in the group based on quantum circuits. In this research, we focus on exploring innovative circuit design for implementing interesting  physics using the microwave supeconducting quantum circuit platform. (Image credit Marios Kounalakis)

Related publications:

Observation and stabilization of photonic Fock states in a hot radio-frequency resonator
Mario F. Gely, Marios Kounalakis, Christian Dickel, Jacob Dalle, Rémy Vatré, Brian Baker, Mark D. Jenkins, Gary A. Steele
Science 363, 1072 (2019) arxiv

Tuneable hopping and nonlinear cross-Kerr interactions in a high-coherence superconducting circuit
M. Kounalakis, C. Dickel, A. Bruno, N. K. Langford, G. A. Steele
npj Quantum Information 4, 38 (2018) arxiv