4 research outputs found
Quantum trajectories and their statistics for remotely entangled quantum bits
We experimentally and theoretically investigate the quantum trajectories of
jointly monitored transmon qubits embedded in spatially separated microwave
cavities. Using nearly quantum-noise limited superconducting amplifiers and an
optimized setup to reduce signal loss between cavities, we can efficiently
track measurement-induced entanglement generation as a continuous process for
single realizations of the experiment. The quantum trajectories of transmon
qubits naturally split into low and high entanglement classes corresponding to
half-parity collapse. The distribution of concurrence is found at any given
time and we explore the dynamics of entanglement creation in the state space.
The distribution exhibits a sharp cut-off in the high concurrence limit,
defining a maximal concurrence boundary. The most likely paths of the qubits'
trajectories are also investigated, resulting in three probable paths,
gradually projecting the system to two even subspaces and an odd subspace. We
also investigate the most likely time for the individual trajectories to reach
their most entangled state, and find that there are two solutions for the local
maximum, corresponding to the low and high entanglement routes. The theoretical
predictions show excellent agreement with the experimental entangled qubit
trajectory data.Comment: 11 pages and 4 figure
Quantum trajectories of superconducting qubits
International audienc
Hybrid quantum-classical hierarchy for mitigation of decoherence and determination of excited states
Using quantum devices supported by classical computational resources is a promising approach to quantum-enabled computation. One powerful example of such a hybrid quantum-classical approach optimized for classically intractable eigenvalue problems is the variational quantum eigensolver, built to utilize quantum resources for the solution of eigenvalue problems and optimizations with minimal coherence time requirements by leveraging classical computational resources. These algorithms have been placed as leaders among the candidates for the first to achieve supremacy over classical computation. Here, we provide evidence for the conjecture that variational approaches can automatically suppress even nonsystematic decoherence errors by introducing an exactly solvable channel model of variational state preparation. Moreover, we develop a more general hierarchy of measurement and classical computation that allows one to obtain increasingly accurate solutions by leveraging additional measurements and classical resources. We demonstrate numerically on a sample electronic system that this method both allows for the accurate determination of excited electronic states as well as reduces the impact of decoherence, without using any additional quantum coherence time or formal error-correction codes