NANOMAGIQC

Project Objectives

Objective No. 4: Entanglement and Gates

Entanglement between different qubits is a key objective for any QC hardware candidate. This requires a Hamiltonian of interaction between two qubits.

In this project we aim to evaluate the entanglement between the quantum states of the different magnetic entities by connecting them by superconducting lines with Josephson switches.

One-qubit gates would be tested by performing Rabi oscillations using the fact that it is possible to fit the energy gap in the clusters and particles to the SQUID frequency.

In the case of two-qubit gates, the entanglement between two qubits will beswitched on and off using the principle which underlies the operation of so-calledquantum roulette noise thermometer.

This involves a parallel combination of two Josephson junctions, enclosing a low inductance loop. Provided that the ratio of the junction critical currents to inductance is sufficiently small, the application of a half magnetic flux quantum to the loop can suppress the superconductivity in the loop by several orders of magnitude. Thus the device can act as a rapid, dissipationless switch.

The quantification of entanglement, both in experimental and simulated results, can be made through state tomography.

It should be noted that such work has already been performed in photonic and atom/ion systems, for which the qubit scalability is limited.

However, our aims,

• to perform Rabi oscillations of spin states,
• to entangle magnetic qubits, and
• to couple nanoparticles and microSQUIDs,

would demonstrate the basis for quantum computing in a condensed matter system with the potential for scalability in qubit number.

This would be a first in Europe and success would put our labs in the pole position for the fabrication of quantum nanodevices.

Moreover, overcoming the technical difficulties in controlling the dissipation in the ON/OFF switching of the Josephson junctions will be a significant breakthrough infast operation techniques. This will have important consequences for the wider European scientific and technological communities in which such techniques are employed.