Abstract
Condensed matter physics has been driven forward by significant experimental and theoretical progress in the study and understanding of equilibrium phase transitions based on symmetry and topology. However, nonequilibrium phase transitions have remained a challenge, in part due to their complexity in theoretical descriptions and the additional experimental difficulties in systematically controlling systems out of equilibrium. Here, we study a one-dimensional chain of 72 microwave cavities, each coupled to a superconducting qubit, and coherently drive the system into a nonequilibrium steady state. We find experimental evidence for a dissipative phase transition in the system in which the steady state changes dramatically as the mean photon number is increased. Near the boundary between the two observed phases, the system demonstrates bistability, with characteristic switching times as long as 60 ms—far longer than any of the intrinsic rates known for the system. This experiment demonstrates the power of circuit QED systems for studying nonequilibrium condensed matter physics and paves the way for future experiments exploring nonequilbrium physics with many-body quantum optics.
- Received 10 August 2016
DOI:https://doi.org/10.1103/PhysRevX.7.011016
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Over the years, the study of phase transitions has steadily advanced the field of condensed matter physics. A phase transition denotes a sudden change in the physical properties of a system as a function of an external parameter, such as liquid freezing into solid as temperature decreases below the freezing point. Much of our understanding of phase transitions is limited to systems at equilibrium, with no flux of energy or particles over time. This assumption is rarely true, but finding phase transitions in nonequilibrium systems has remained a challenge because such systems are difficult to control. Interacting photons (particles of light) have emerged as an excellent candidate for studying nonequilibrium physics because of their innate property to leak out of any system and the ease with which they can be added back in. Here, we present experimental evidence for a nonequilibrium phase transition in which the steady state of a system changes dramatically as the mean photon number is increased.
Photons do not interact with each other ordinarily, but strong coupling between atoms and a cavity can mediate effective photon-photon interactions. In circuit quantum electrodynamics (circuit QED), we can engineer these interactions using superconducting microwave cavities and quantum bits (qubits). We study a circuit QED lattice made of a one-dimensional chain of 72 cavities, each coupled to a qubit. Phase transitions are characterized by transmitting a microwave signal of varying frequency and power through the circuit and measuring the power of the output signal.
This experiment demonstrates the power of circuit QED systems for studying nonequilibrium condensed matter physics and paves the way for future experiments on exotic states of many interacting photons.