Room-temperature entanglement between single defect spins in diamond

Abstract

and macroscopic diamond 10 . Here we experimentally demonstrate entanglement between two engineered single solid-state spin quantum bits (qubits) at ambient conditions. Photon emission of defect pairs reveals ground-state spin correlation. Entanglement (fidelity = 0.67 ± 0.04) is proved by quantum state tomography. Moreover, the lifetime of electron spin entanglement is extended to milliseconds by entanglement swapping to nuclear spins. The experiments mark an important step towards a scalable room-temperature quantum device being of potential use in quantum information processing as well as metrology.Engineering entangled quantum states is a decisive step in quantum technology. Although entanglement among weakly interacting systems such as photons has been demonstrated already in the early stages of quantum optics, deterministic generation of entanglement in more complex systems such atoms or ions, not to mention solids, is a relatively recent achievement 11 . Usually in solid-state systems rapid dephasing ceases any useful degree of quantum correlations. Either decoupling must be used to protect quantum states or careful materials engineering is required to prolong coherence. Most often however, and this is especially important for solid-state systems, one needs to resort to low (milliKelvin) temperatures to achieve sufficiently robust and longlasting quantum coherence. Spins are sufficiently weakly coupled to their environment to allow for the observation of coherence at room temperatures.Diamond defect spins are particularly interesting solid-state spin qubit systems. A number of hallmark demonstrations such as single-, two-and three-qubit operations, high-fidelity single-shot readout 12 , one-and two-qubit algorithms 13 , and entanglement between nuclear and electron and nuclear spin qubits have been achieved 6,14 . Different schemes to scale the system to a larger number of entangled electron spins have been proposed [15][16][17] . A path towards room-temperature entanglement is strong coupling among the ground-state spin magnetic dipole moment of adjacent defects centres. This mutual dipolar interaction scales as distance d −3 and should be larger than the interaction of each electron spin with the residual paramagnetic impurities or nuclear spin moments in the lattice (Fig. 1d). Typical cutoff distances for strong interaction are thus limited by the electron spin dephasing time (milliseconds) to be around 30 nm. Here we demonstrate entanglement between two electron and nuclear spins at a distance of approximately 25 nm. At these distances magnetic dipole coupling is strong enough to attain high-fidelity entanglement while being able to address the spins individually by super-resolution optical microscopy 18 . The optical as well as spin physics of nitrogen vacancy (NV) defects in diamond has been subject to numerous investigations 11,19 . The fluorescence intensity of the strongly allowed optical transition between ground and excited spin triplet states depends on the magnetic quantum number of the groun...

Decay of the rotary echoes for the spin of a nitrogen-vacancy center in diamond

“…The approximation is base on the assumption, λ ≪ ω. At the same time, its accuracy is guaranteed only when ψ > λ/ω, where ψ has a short-time asymptotics (23) [cf. Eq.…”

“…Among these systems, the nitrogen-vacancy (NV) centers in diamond exhibit a set of particularly desirable features: individual centers can be initialized and read out optically, 1-4 possess naturally long coherence times even at room temperature, [5][6][7] and can be controlled 8 using magnetic fields, 9-12 optical excitations, [13][14][15][16][17] and electric fields. [18][19][20] As a result, the NV centers have attracted much attention as prospective qubits for quantum information processing, 4,7,15,16,[21][22][23][24][25] and as nanoscale sensors. 20,[26][27][28][29][30][31][32][33][34][35][36][37][38] Efficiency of the NV-based devices critically depends on the NV spin coherence time, which is controlled by the coupling to the spins of substitutional nitrogen atoms and/or to the bath of 13 C nuclear spins.…”

Nonlinear optical signals and spectroscopy with quantum light

“…Different degrees of freedom of light can become entangled. Most common types of entanglement are: their spin (Dolde et al, 2013), polarization (Shih and Alley, 1988), position and momentum , time and energy (Tittel et al, 1999), etc. Entangled photon pairs constitute an invaluable tool in fundamental tests of quantum mechanics -most famously in the violation of Bell's inequalities (Aspect et al, 1982a(Aspect et al, , 1981(Aspect et al, , 1982b or in Hong, Ou and Mandel's photon correlation experiments (Hong et al, 1987;Ou and Mandel, 1988;Shih and Alley, 1988).…”

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

“…[9][10][11] To further extend the study of the interaction between a multi-NV center and the nanoscale sensing with the NV center, it is necessary to detect and control the NV center spin-state dynamics with high spatial resolution. 7,[12][13][14] Therefore, many optical super-resolution microscopy techniques have been developed to detect single NV centers. [13][14][15][16][17] Among these methods, stimulated emission depletion (STED) microscopy 12,[18][19][20] is one of the most promising.…”