Deep Three-Dimensional Solid-State Qubit Arrays with Long-Lived Spin Coherence

Abstract

Three-dimensional arrays of silicon transistors increase the density of bits 1 . Solid-state qubits are much larger so could benefit even more from using the third dimension given that useful fault-tolerant quantum computing will require at least 100,000 physical qubits and perhaps one billion 2 . Here we use laser writing to create 3D arrays of nitrogen-vacancy centre (NVC) qubits in diamond. This would allow 5 million qubits inside a commercially available 4.5x4.5x0.5 mm diamond based on five nuclear qubits per NVC 3,4 and allowing (10 µm) 3 per NVC to leave room for our laser-written electrical control. The spin coherence times we measure are an order of magnitude longer than previous laser-written qubits 5 and at least as long as non-laser-written NVC 6 . As well as NVC quantum computing 3,4,6-8 , quantum communication 7,9,10 and nanoscale sensing 11-14 could benefit from the same platform. Our approach could also be extended to other qubits in diamond 15-18 and silicon carbide 19,20 .Demonstrated qubit fidelities 8 for a single negatively-charged nitrogen vacancy centre (NVC) and its nearby nuclear spins are above the required thresholds for quantum computing 2 . Two NVCs in different diamonds, in separate cryostats, have been optically entangled faster than the decoherence of this entanglement 7 , but it will not be practical to have 10 6 cryostats for 10 6 NVCs. In the transparent lattice of wide-band-gap diamond, individual opticallyaddressable qubits can fill a volume rather than be restricted to the surface. For computation, a 3D array spanning the upper 50 µm of a commercially-available electronic (EL) grade 4.5×4.5×0.5 mm diamond could contain 10 6 NVCs with (10 µm) 3 for each NVC. Each NVC has, on average, five individually-addressable 13 C nuclear spin qubits 3,4 . For communications, having an array of NVCs will provide many spin-photon interfaces within one cryostat 10 , increasing data rates and allowing multiplexing. Sensing with 2D arrays of NVCs will combine the high resolution of single NVC sensing 11 with the simultaneous imaging achieved with wide-field microscopy 13 . Stacking two of these 2D arrays will then permit gradiometry which will increase the sensitivity by subtracting the background noise measured by the array that is further from the sample of interest.

Barrier potential for laser written graphitic wires in diamond

“…Evaluation of the barrier potential will be an important factor when characterising new schemes for laser processing wires, such as the use of Bessel beams [25,26]. The barrier potential is also a highly relevant consideration as more complicated device architectures utilising laser written wires in diamond start to emerge, with designs comprising wire junctions [27] and intentional gaps in the conductive network [28].…”

Laser Writing of Scalable Single Color Centers in Silicon Carbide

“…The yield of optically stable single VSi centres is up to 30%. In diamond, some form of annealing is always required to generate NVcentres [20][21][22]. On the contrary, single VSi centres in SiC can be created with just a single pulse and no annealing.…”

Preparations and applications of single color centers in diamond

“…This method can achieve the precise positioning of array of single NV color center in diamond, and its spatial resolution accuracy reaches 33 nm [78]. However, these accurately prepared individual color centers are far away from the crystal surface (> 10 μm) [79], which limits the sensitivity of magnetic field and temperature measurements [80].…”