Quantum register based on coupled electron spins in a room-temperature solid

Abstract

Devices that harness the laws of quantum physics hold the promise for information processing that outperforms their classical counterparts, and for unconditionally secure communication 1 . However, in particular, implementations based on condensed-matter systems face the challenge of short coherence times. Carbon materials 2,3 , particularly diamond 4-6 , however, are suitable for hosting robust solid-state quantum registers, owing to their spin-free lattice and weak spin-orbit coupling. Here we show that quantum logic elements can be realized by exploring long-range magnetic dipolar coupling between individually addressable single electron spins associated with separate colour centres in diamond. The strong distance dependence of this coupling was used to characterize the separation of single qubits (98±3 Å) with an accuracy close to the value of the crystal-lattice spacing. Our demonstration of coherent control over both electron spins, conditional dynamics, selective readout as well as switchable interaction should open the way towards a viable room-temperature solid-state quantum register. As both electron spins are optically addressable, this solid-state quantum device operating at ambient conditions provides a degree of control that is at present available only for a few systems at low temperature.One of the greatest challenges in quantum information technology is to build a room-temperature scalable quantum processor 7 . Isolated electron and nuclear spins in solids are considered to be among the most promising candidates for qubits in that respect 3,8 . Several benchmark experiments including entanglement and elements of quantum memory 9 have been achieved with spin ensembles, but ultimate functionality requires encoding quantum information into single spins. This however creates serious challenges in readout, addressing and nano-engineering single-spin arrays. The availability of photon-assisted single-spin readout 10,11 and the possibility to create single defects by ion implantation 12,13 make nitrogen-vacancy defects in diamond one of the most promising candidates in this respect. Paramagnetic nuclei in the vicinity of the electron spin can be used as auxiliary qubits with even more favourable relaxation properties 14 . As a consequence, coherence between electron and nuclear spin qubits has been exploited for showing all basic elements of a room-temperature quantum register 5,[15][16][17] . The size of these registers however is limited to a few quantum bits owing to the limited number of nuclear spins that can be addressed in frequency space 15,18 . A critical step towards scalability is to develop a technique enabling mutual coupling of individual optically addressable quantum systems. The system used in this study is a pair of single electron spins associated with separate nitrogen-vacancy defects in diamond. A single defect consists of a substitutional nitrogen atom in the diamond lattice and an adjacent vacancy (Fig. 1a,b). The electron spin triplet ground state of the defect shows a spin-depen...

Subdiffraction optical manipulation of the charge state of nitrogen vacancy center in diamond

“…Because charge-state conversion changes the local field in diamond, 2,26 the CSD microscopy method can potentially be used for the study of spin-state quantum coherent dynamics and the interaction between coupled spin systems in diamond. 2,13,31 …”

Magnetic spin imaging under ambient conditions with sub-cellular resolution

“…Precision metrology has already been demonstrated for DC and AC fields [9][10][11][12][13][14] , spins within the diamond lattice [15][16][17][18] and surface spins 19 . Here, we demonstrate sensing and imaging of stochastic magnetic fluctuations originating from freely diffusing electron spins such as paramagnetic oxygen (O 2 , S ¼ 1), MnCl 2 (S ¼ 5/2) and Gadolinium ions (Gd 3 þ , S ¼ 7/2) in liquids, immobilized in polymers and linked specifically to cellular structures.…”

One- and two-dimensional photonic crystal microcavities in single crystal diamond

“…Local coupling between NV − qubits can be mediated by magnetic interactions [2], whereas long-distance coupling might rather be promoted by optical interactions [3]. Such transfer of quantum information between spins and photons in solid state systems [4] can be strongly enhanced by optical microcavities with small mode volume V mod and large quality factor Q. Micro-cavities can further be employed for enhancing the emission rate of single photon emitters [5,6] based e.g.…”