13 research outputs found
Pfaffian formula for fermion parity fluctuations in a superconductor and application to Majorana fusion detection
Kitaev's Pfaffian formula equates the ground-state fermion parity of a closed
system to the sign of the Pfaffian of the Hamiltonian in the Majorana basis.
Using Klich's theory of full counting statistics for paired fermions we
generalize the Pfaffian formula to account for quantum fluctuations in the
fermion parity of an open subsystem. A statistical description in the framework
of random-matrix theory is used to answer the question when a vanishing fermion
parity in a superconductor fusion experiment becomes a distinctive signature of
an isolated Majorana zero-mode.Comment: 11 pages, 6 figure
Voltage staircase in a current-biased quantum-dot Josephson junction
We calculate the current-voltage (I-V) characteristic of a Josephson junction
containing a resonant level in the weakly coupled regime (resonance width small
compared to the superconducting gap). The phase across the junction
becomes time dependent in response to a DC current bias. Rabi oscillations in
the Andreev levels produce a staircase I-V characteristic. The number of
voltage steps counts the number of Rabi oscillations per increment of
, providing a way to probe the coherence of the qubit in the absence of
any external AC driving. The phenomenology is the same as the "Majorana-induced
DC Shapiro steps in topological Josephson junctions" of Phys. Rev. B 102,
140501(R) (2020) -- but now for a non-topological Andreev qubit.Comment: 7 pages, 7 figures, Appendix adde
Ultrafast dynamics of cold Fermi gas after a local quench
We consider non-equilibrium dynamics of two initially independent reservoirs
and filled with a cold Fermi gas coupled and decoupled by two quantum
quenches following one another. We find that the von Neumann entropy production
induced by the quench is faster than thermal transport between the reservoirs
and defines the short-time dynamics of the system. We analyze the energy change
in the system which adds up the heat transferred between and and the
work done by the quench to uncouple the reservoirs. In the case when and
interact for a short time, we notice an energy increase in both reservoirs
upon decoupling. This energy gain results from the quench's work and does not
depend on the initial temperature imbalance between the reservoirs. We relate
the quench's work to the mutual correlations of and expressed through
their von Neumann entropies. Utilizing this relation, we show that once and
become coupled, their entropies grow (on a timescale of the Fermi time)
faster than the heat flow within the system. This result may provide a track of
quantum correlations' generation at finite temperatures which one may probe in
ultracold atoms, where we expect the characteristic timescale of correlations'
growth to be .Comment: 12 pages, 6 figures (published version
Quantum tunneling dynamics in a complex-valued Sachdev-Ye-Kitaev model quench-coupled to a cool bath
Theoretical Physic
Dynamical signatures of ground-state degeneracy to discriminate against Andreev levels in a Majorana fusion experiment
Theoretical Physic
Energy dynamics, information and heat flow in quenched cooling and the crossover from quantum to classical thermodynamics
Abstract The dynamics when a hot many-body quantum system is brought into instantaneous contact with a cold many-body quantum system can be understood as a combination of early time quantum correlation (von Neumann entropy) gain and late time energy relaxation. We show that at the shortest timescales there is an energy increase in each system linked to the entropy gain, even though equilibrium thermodynamics does not apply. This energy increase is of quantum origin and results from the collective binding energy between the two systems. Counter-intuitively, this implies that also the hotter of the two systems generically experiences an initial energy increase when brought into contact with the other colder system. In the limit where the energy relaxation overwhelms the (quantum) correlation build-up, classical energy dynamics emerges where the energy in the hot system decreases immediately upon contact with a cooler system. We use both strongly correlated SYK systems and weakly correlated mixed field Ising chains to exhibit these characteristics, and comment on its implications for both black hole evaporation and quantum thermodynamics