Realization of devices based on quantum laws might lead to building processors that outperform their classical analogues and establishing unconditionally secure communication protocols. Solids do usually present a serious challenge to quantum coherence. However, owing to their spin-free lattice and low spin orbit coupling, carbon materials and particularly diamond are suitable for hosting robust solid state quantum registers. We show that scalable quantum logic elements can be realized by exploring long range magnetic dipolar coupling between individually addressable single electron spins associated with separate color centers in diamond. Strong distance dependence of coupling was used to characterize the separation of single qubits 98 A with unprecedented accuracy (3 A) close to a crystal lattice spacing. Our demonstration of coherent control over both electron spins, conditional dynamics, selective readout as well as switchable interaction, opens the way towards a room temperature solid state scalable quantum register. Since both electron spins are optically addressable, this solid state quantum device operating at ambient conditions provides a degree of control that is currently available only for atomic systems.
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