Physics Colloquium Presents Jonathan R. Friedman

Join us for the first Physics Colloquium of the semester with Jonathan R. Friedman, Amherst College, as he presents "When a clock (transition) is good for more than telling time." Dinner will be at 5 p.m. with the talk starting at 6 p.m. Students are encouraged to meet with Prof. Friedman at 4 p.m. in Park 336.

About Jonathan R. Friedman

The burgeoning field of quantum information requires precise control of the quantum state of a qubit. Quantum states are generally described by complex amplitudes in which a well-defined phase is paramount.  When information about the state’s phase is lost to the qubit’s environment – a process known as decoherence – the utility of the state for quantum information applications is also lost. Thus, protecting a qubit from the effects of its environment is important in nearly all aspects of quantum information science. One method of achieving decoupling of a system from its environment is through the use of so-called clock transitions, a name arising from their original use in precision atomic clocks. A clock transition occurs at an avoided level crossing where the transition frequency is independent (to first order) of an external perturbation, such as a fluctuating magnetic field. In spin-qubit systems, a bath of environmental spins can lead to decoherence and a suppression of T₂, the characteristic phase decoherence time. In molecular nanomagnets, which are chemically synthesized spin systems, clock transitions can be engineered by exploiting the symmetry of the molecule. I will discuss how T₂ can be markedly enhanced by clock transitions in some molecular nanomagnets, suggesting these systems can be viable spin qubits. The study of such systems can also elucidate the mechanisms of decoherence since spin-spin interactions are suppressed at a clock transition, allowing us to isolate the decohering effects of such interactions from those due to other mechanisms.

Physics