Faculty @ Aalto University, Finland

Wednesday June 29 – 10.45 BST

Counting electrons and photons in nanocircuits – experiments on non-equilibrium thermodynamics 

I describe recent experiments in our laboratory on how non-equilibrium excitations in low temperature superconductors can be observed by counting emitted electrons one-by-one [1]. Interesting statistics and long-term relaxation of rare events reveal new features of quasiparticle excitations in the system, precisely characterized in the experiment, but not fully in line with earlier understanding. In the second part of the talk I describe our current efforts to move from steady-state bolometric measurements of thermal microwave photons [2] to observation of single events by a nano-calorimeter. I describe the sensitive thermometer on the electronic absorber of this calorimeter achieving the fundamental lower bound of energy fluctuations arising from fluctuation-dissipation theorem [3]. The detector is in principle capable of detecting absorption events of single photons in a circuit in a continuous manner. We describe a recent proposal of splitting the energy of the photon to two absorbers to significantly boost the signal-to-noise ratio in a temperature cross-correlation measurement [4]. 

[1] E. T. Mannila, P. Samuelsson et al., Nat. Phys. 18, 145 (2022). 
[2] JP and Bayan Karimi, Rev. Mod. Phys. 93, 041001 (2021). 
[3] Bayan Karimi et al., Nat. Commun. 11, 367 (2020). 
[4] JP and Bayan Karimi, Phys. Rev. X 12, 011026 (2022).