The Design of a Scalable and Distributed Quantum Information
Processor in Diamond

William J. Munro1, Michael Trupke2, Simon J. Devitt3, Ashley M. Stephens3,
Burkhard Scharfenberger3, Kathrin Buczak2, Tobias Nöbauer2, Mark S. Everitt3,
Jörg Schmiedmayer2, and Kae Nemoto3
1Optical Science Laboratory, 2TU Wien, 3NII

Physics and information are intimately connected together. It is now widely accepted that the ultimate “information” processing devices will be those that harness and utilize the principles of quantum mechanics. There have been many physical systems identified that can be used for such processing [1]. Many proof of principle experiments have been performed, but none of these are immune from errors. One needs to find a path from today’s experiments to tomorrow’s scalable quantum computers and communication networks. Here, we develop an architecture based on a simple quantum module comprising an optical cavity containing a single negatively charged nitrogen vacancy center (NV-) in diamond. The modules can be connected together by photons propagating in an optical fiber network and thus collectively used to generate a topological cluster state, a robust substrate for quantum information processing. We show that this architecture enables us to start with a few modules and scale up to large capacity quantum information processing with existing technology [2].

The module at the center of this approach is depicted in Fig. 1(a) where the cavities mediate interactions between the photons and the electron spins. The electron spins are coupled to nuclear spins: the later constitute long-lived quantum memories where quantum information is stored and processed. The electron spin is acting as an interface between the nuclear spin and optical photons. Entanglement can be generated between two modules using a single photon propagating in the fiber-optical network [Fig. 1(a)]. The scheme works by dividing a photon on a 50/50 beam splitter and sending each half to a module where it interacts (gaining a phase shift if the electron spin is in its |1> state). The reflected photon parts from each module are then recombined on the beam splitter and the dark port measured. If the detector clicks, entanglement has been generated between the electron spins in each module [2]. This entanglement is then transferred to the nuclear spins creating a long-lived link between the modules. Once this has been done entanglement generation can be attempted with further modules allowing a large-scale cluster state to be generated [Fig. 1(b)]. Such a resource is useful for universal quantum computation and long-range quantum communication.

This work was supported in part by NICT.

T. D. Ladd et al., Nature 464, 45 (2010).
K. Nemoto et al., Phys. Rev. X 4, 031022 (2014).

Fig. 1. NV center based quantum architecture. (a) Entanglement of two quantum modules using a single photon interferometer (inset shows the energy level structure of the NV center). (b) Entanglement between many modules creating a 3D lattice for general quantum computation and communication.