University of St Andrews
School of Physics and Astronomy
We are theoretical condensed matter physicists interested in many-body
and interaction effects
in systems that are attractive for future quantum technology.
Our current activities involve:
Topological states by self-organisation transitions in interacting low-dimensional conductors.
New physics achievable with Majorana bound states in condensed matter systems.
Generation and detection of entanglement in nanostructures.
For details on our recent activities click here.
Potential post-doc or PhD applicants: please look here.
Latest papers by the group
Coherent backaction between spins and an electronic bath: Non-Markovian dynamics and low temperature quantum thermodynamic electron cooling
S. Matern, D. Loss, J. Klinovaja, B. Braunecker
We provide a general analytical framework for calculating the dynamics of a spin system in contact with a bath beyond the Markov
approximation. The approach is based on a systematic expansion of the Nakajima-Zwanzig master equation in the weak-coupling limit
but makes no assumption on the time dynamics and includes all quantum coherent memory effects leading to non-Markovian dynamics.
Our results describe, for the free induction decay, the full time range from the non-Markovian dynamics at short times, to the
well-known exponential thermal decay at long times. We provide full analytic results for the entire time range using a bath of
itinerant electrons as an archetype for universal quantum fluctuations. Furthermore, we propose a quantum thermodynamic scheme to
employ the temperature insensitivity of the non-Markovian decay to transport heat out of the electron system and thus, by repeated
re-initialisation of a cluster of spins, to efficiently cool the electrons at very low temperatures.
Non-Equilibrium Charge Dynamics in Majorana-Josephson Devices
I. J. van Beek, A. Levy Yeyati, B. Braunecker
Phys. Rev. B 98, 224502 (2018)
We investigate the impact of introducing Majorana bound states, formed by a proximitized semiconducting
nanowire in the topological regime, into a current biased capacitive Josephson junction, thereby adding
delocalized states below the superconducting gap. We find that this qualitatively changes the charge
dynamics of the system, diminishing the role of Bloch oscillations and causing single-particle tunneling
effects to dominate. We fully characterize the resulting charge dynamics and the associated voltage and
current signals. Our work reveals a rich landscape of behaviors in both the static and time-varying
driving modes. This can be directly attributed to the presence of Majorana bound states, which serve as
a pathway for charge transport and enable nonequilibrium excitations of the Majorana-Josephson device.