The LIGO detection of gravitational waves has opened a new window on the universe. I will discuss how the process of superradiance, combined with gravitational wave measurements, makes black holes into nature's laboratories to search for new light bosons, from axions to dark photons. When a bosonic particle's Compton wavelength is comparable to the horizon size of a black hole, superradiance of these bosons into `hydrogenic' bound states extracts energy and angular momentum from the black hole. The occupation number of the levels grows exponentially and the black hole spins down. One candidate for such an ultralight boson is the QCD axion with decay constant above the GUT scale. Current black hole spin measurements disfavor a factor of 30 (400) in axion (vector) mass; future measurements can provide evidence of a new boson. Particles transitioning between levels and annihilating to gravitons may produce thousands of monochromatic gravitational wave signals, and turn LIGO into a particle detector.
Tremendous progress has been achieved in the coherent control of single quantum states (single charges, phonons, photons, and spins). At the frontier of quantum information science are efforts to hybridize different quantum degrees of freedom. For example, by coupling a single photon to a single electron fundamental light-matter interactions may be examined at the single particle level to reveal exotic quantum effects, such as single atom lasing. Coherent coupling of spin and light, which has been the subject of many theoretical proposals over the past 20 years, could enable a quantum internet where highly coherent electron spins are used for quantum computing and single photons enable long-range spin-spin interactions. In this colloquium I will describe experiments where we couple a single spin in silicon to a single microwave frequency photon. The coupling mechanism is based on spin-charge hybridization in the presence of a large magnetic field gradient. Spin-photon coupling rates gs/2p > 10 MHz are achieved and vacuum Rabi splitting is observed in the cavity transmission, indicating single spin-photon strong coupling. These results open a direct path toward entangling single spins at a distance using microwave frequency photons.
About the speaker
Jason Petta's research group focuses on quantum control of nanometer scale systems. Semiconductor quantum dots are used to isolate single electron spins, which exhibit long quantum coherence times. These systems allow quantum mechanics to be harnessed in a solid state environment for the implementation of quantum gates. They use nanofabrication to create artificially structured systems with experimentally tunable Hamiltonians that can be controlled on sub-nanosecond timescales. Recent research examines strong light-matter interactions in the circuit quantum electrodynamics architecture, with a goal of generating long-range many body entanglement. Silicon and diamond are ideal host materials for spin coherence, leading to spin coherence times that now approach 10 seconds. A major effort in the group consists of developing a scalable quantum computing architecture in isotopically purified silicon. Research advances are enabled by a tight feedback loop that links nanoscale materials synthesis and advanced transport measurements.
The superconductor-insulator transition exhibits a remarkable duality symmetry directly relating the resistance measured in the superconducting regime to the conductance measured in the insulator. This symmetry points to a deep relation between these two seemingly-opposing phases. At very low temperatures (below 200 mK for our amorphous indium-oxide films) this beautiful symmetry is severely violated. We demonstrate that this violation is associated with the emergence of a new insulating ground-state in which the electrons are effectively decoupled from the host phonons. We further show that duality symmetry can be effectively restored by driving the system out of equilibrium.