Quantum Information with NV Centres

The aim of QINVC is to exploit the superior quantum coherence of the spins of the negatively charged Nitrogen-Vacancy (NV) colour centres in diamond, at both room and low temperature, for quantum information processing (QIP). This system is indeed among the best solid-state quantum systems in terms of coherence, ease of manipulation by ESR, and addressability down to the single spin using optical microscopy. Our project first focuses on two hybrid strategies for QIP (WP1). The first one consists in fabricating regular arrays of single NV centres, with gate operation performed using a movable NV spin placed at the apex of a cantilever, coming close enough to get entangled with a NV spin on the lattice using magnetic dipolar interaction. The fabrication method is based on pulsed ion beam implantation through a tiny hole threading the tip of an AFM cantilever, or through the voids of a mask deposited at the surface of the diamond sample. The second strategy implements a hybrid architecture for QIP based on circuit QED and ensembles of NV spins: transmon qubits are coupled to ensembles of NV spins through the resonator in which they are embedded. The NV spins will be used as a long-coherence time quantum memory for the transmon qubits which will be used to process quantum information.

QINVC will investigate in WP2 the optical properties of NV centres at low temperature. The first goal of WP2 is to transfer the optical techniques used at room temperature to control electron and nuclear spins to low-temperatures, in the purpose of applying them to hybrid quantum circuits (WP1). A second goal is to investigate the potential of NV centres ensembles to build a quantum memory for optical photons. These ambitious goals will request the optimisation of NV centre production and their spin properties in synthetic diamond (WP3) using state-of-the-art methods and beyond. This will be done in collaboration with the world industrial leader on the production of synthetic diamond Element6 Ltd. Engineered implantation of single N impurities with nanometer resolution will be performed for WP1, and suitable concentrations will be prepared for both WP1 and WP2. Sample processing will be developed for these two WPs in order to minimize the unwanted defects that cause decoherence. Innovative fabrication techniques will be also developed, such as the preferential alignment of NV centres under uniaxial stress, an appealing possibility.

The QINVC project is a frontier research project that aims at developing a quantum technology in the domain of quantum information. Indeed, quantum mechanics does make a difference with classical physics in this domain. Although present day research is still very far from providing useful quantum processors, the impact of the QINVC project is sizeable. The project will impact on all academic and industrial researchers striving to exploit the remarkable properties of the NV centre.

An innovative road towards Quantum Information: hybrid structures Despite about a decade of intensive research, the systems investigated up to now do not match all the required criteria for making quantum processors. The innovative research on hybrid structures proposed by our QINVC consortium offers a chance to succeed where other systems have not. Is it possible to take the best of the microscopic quantum systems, namely their superior quantum coherence, and of the quantum electrical circuits, namely their ease of operation? QINVC will probe the whole issue of the hybrid way for quantum information.

Linking microscopic entities to macroscopic objects
In the wider context of quantum physics, the primary outcome will be to establish a direct link between microscopic entities, the NV spins, and macroscopic electrical circuits. Although quantum mechanics rules both worlds, they are not very often in speaking terms. This is what QINVC will achieve, and this would have an impact on our understanding of quantum mechanics.

Innovative truly quantum materials
On the material side, improving materials with a well affirmed quantum character is also very important. Indeed, quantum properties of NV centres are not only considered for quantum information, but also for numerous applications. Sample optimisation and characterisation will thus have an impact in other more applied areas such as magnetometry or magnetic microscopy. The close link already established with Element Six Ltd will be very useful in this respect.