Parity detection and entanglement with a Mach-Zehnder interferometer

TL;DR

This paper demonstrates how a Mach-Zehnder interferometer coupled with double quantum dots can function as an ideal parity meter, enabling entanglement of charge qubits with maximal efficiency through charge current measurements.

Contribution

It introduces a method to use a Mach-Zehnder interferometer as an efficient parity detector for charge qubits, facilitating entanglement without mutual interaction between qubits.

Findings

The setup detects two parity classes via two currents, simplifying measurement.

The MZI acts as an ideal, maximally efficient parity detector.

Unentangled initial states can become entangled with probability one.

Abstract

A parity meter projects the state of two qubits onto two subspaces with different parities, the states in each parity class being indistinguishable. It has application in quantum information for its entanglement properties. In our work we consider the electronic Mach-Zehnder interferometer (MZI) coupled capacitively to two double quantum dots (DQDs), one on each arm of the MZI. These charge qubits couple linearly to the charge in the arms of the MZI. A key advantage of an MZI is that the qubits are well separated in distance so that mutual interaction between them is avoided. Assuming equal coupling between both DQDs and the arms and the same bias for each DQD, this setup usually detects three different currents, one for the odd states and two for each even state. Controlling the magnetic flux of the MZI, we can operate the MZI as a parity meter: only two currents are measured at the output, one for each parity class. In this configuration, the MZI acts as an ideal detector, its Heisenberg efficiency being maximal. For a class of initial states, the initially unentangled DQDs become entangled through the parity measurement process with probability one.