Flight of the qubit

Charles Q. Choi

Eugene Polzik

A trapped ion emits a photon. Ion and photon are entangled, so the photon carries away information on the state of the ion. Now realized, this system could become a communication link in a quantum network.

Arnab Dey

Yahui Chai, Lena Funcke, Tobias Hartung +4 more

We investigate the performance of the variational quantum eigensolver (VQE) for the problem of optimal flight-gate assignment. This is a combinatorial-optimization problem that aims at finding an optimal assignment of flights to the gates of an airport, in order to minimize the passenger travel time. To study the problem, we adopt a qubit-efficient binary encoding with a cyclic mapping, which is suitable for a digital quantum computer. Using this encoding in conjunction with the conditional value at risk (CVaR) as an aggregation function, we systematically explore the performance of the approach by classically simulating the CVaR VQE. Our results indicate that the method allows for finding a good solution with high probability and that it significantly outperforms the naive VQE approach. We examine the role of entanglement for the performance and find that ans\"atze with entangling gates allow for better results than pure product states. Studying the problem for various sizes, our numerical data show that the scaling of the number of cost-function calls for obtaining a good solution is not exponential for the regimes that we investigate in this work.

Bernd Konrad, Fabio Di Pumpo, Matthias Freyberger

Abstract An early approach to include pointers representing measurement devices into quantum mechanics was given by von Neumann. Based on this idea, we model such pointers by qubits and couple them to a free particle, in analogy to a classical time-of-flight arrangement. The corresponding Heisenberg dynamics leads to pointer observables whose expectation values allow us to reconstruct the particle’s momentum distribution via the characteristic function. We investigate different initial qubit states and find that such a reconstruction can be considerably simplified by initially entangled pointers. Graphical abstract

Marcus Stephen Edwards