Synthetic quantum matter with interacting photons

Superconducting quantum circuits have recently emerged as a rich platform for probing many-body quantum phenomena. We take advantage of the exquisite control and quantum coherence in these devices to build and study synthetic quantum materials. We directly implement a 1D Bose-Hubbard model using arrays of capacitively coupled superconducting transmon qubits. This system describes the dynamics of interacting particles in a tight-binding lattice. The transmon qubits (blue) serve as lattice sites in which the quantum particles (microwave photons) reside, with intersite tunneling arising from their capacitive coupling, and on-site interactions stemming from their anharmonicity. Our general goal is to develop new techniques for assembling and probing many-body states of light. In previous work, we have harnessed dissipation to stabilize Mott insulators and particle-resolved control to prepare quantum fluids of light. Characterization protocols include interfering coherent superpositions of fluids to extract their thermodynamic properties, and leveraging the precise real-time control of the lattice potential to probe many-body transport dynamics. Upgrading our platform to go beyond 1D and include long-range interactions, we aim to explore novel states of matter potentially useful for quantum information.

Manybody Interferometry of Quantum Fluids

Gabrielle Roberts*, Andrei Vrajitoarea*, Brendan Saxberg, Margaret G Panetta, Jonathan Simon, David I Schuster, Science Adv. 10, 29 (2024)

Disorder-assisted assembly of strongly correlated fluids of light

Brendan Saxberg*, Andrei Vrajitoarea*, Gabrielle Roberts*, Margaret G Panetta, Jonathan Simon, David I Schuster, Nature 612, 435–441 (2022)

Quantum sensing with entangled states of light

Single-photon detection is essential for quantum-limited sensing, quantum communication, and measurement-based quantum computing. In the microwave domain, this task is particularly challenging due to the five orders of magnitude weaker signals compared to optical photons. Implementing single microwave photon detectors offers promising applications in probing & controlling single solid-state spins, enabling the heralded entanglement of remote superconducting qubits in modular architectures, as well as in detecting dark matter candidates such as axions.
We aim to quantum-enhance the signal-to-noise ratio performance of single microwave photon detectors by using arrays of entangled transmon qubits or non-Gaussian photon states in a single microwave resonator, working at the synergistic intersection of quantum error correction and quantum metrology. 

A flux-tunable cavity for Dark Matter detection

Fang Zhao, Ziqian Li, Akash V. Dixit, Tanay Roy, Andrei Vrajitoarea, Riju Banerjee, Alexander Anferov, Kan-Heng Lee, David I. Schuster, Aaron Chou, arXiv:2501.06882 (2025)

Multi-mode cavity QED

The task of building many-body quantum optical platforms has reached a complexity on par with quantum computers: you need to independently control and read out many individual qubits. We explore an alternative architecture where the hardware overhead need not scale with the system size, by coupling only a single or a few qubits to the many cavity modes in a photonic metamaterial. In these tailored metamaterials, the photonic modes are energetically addressable and bestowed with strong photon-photon interactions inherited from the qubit nonlinearity. In this platform, we can utilize parametric interactions between photonic modes to generate multi-mode entangled states of light for quantum information processing, and probe the underlying structure and mode correlations using well-established quantum optics techniques.

Ultrastrong light-matter interaction in a photonic crystal

Andrei Vrajitoarea, Ron Belyansky, Rex Lundgren, Seth Whitsitt, Alexey V Gorshkov, Andrew A Houck, arXiv 2209.14972 (2022)

Chiral cavity quantum electrodynamics

John Clai Owens, Margaret G Panetta, Brendan Saxberg, Gabrielle Roberts, Srivatsan Chakram, Ruichao Ma, Andrei Vrajitoarea, Jonathan Simon, David I Schuster, Nature Physics 18, 1048–1052 (2022)

Quantum control of an oscillator using a stimulated Josephson nonlinearity

Andrei Vrajitoarea, Ziwen Huang, Peter Groszkowski, Jens Koch, Andrew A Houck, Nature Physics 16, 211–217 (2020)