Coherence and entanglement of inherently long-lived spin pairs in diamond

TL;DR

This paper demonstrates that pairs of nuclear spins in diamond can serve as inherently long-lived quantum systems, achieving record coherence times and enabling entanglement for quantum applications.

Contribution

The study reveals that nuclear spin pairs in diamond are naturally protected against decoherence, achieving record coherence times and enabling entanglement with high fidelity.

Findings

Inhomogeneous dephasing time of 1.9 minutes achieved

Long-lived qubits protected by clock transition and decoherence-free subspace

Entangled states realized between spin-pair qubits

Abstract

Understanding and protecting the coherence of individual quantum systems is a central challenge in quantum science and technology. Over the last decades, a rich variety of methods to extend coherence have been developed. A complementary approach is to look for naturally occurring systems that are inherently protected against decoherence. Here, we show that pairs of identical nuclear spins in solids form intrinsically long-lived quantum systems. We study three carbon-13 pairs in diamond and realize high-fidelity measurements of their quantum states using a single NV center in their vicinity. We then reveal that the spin pairs are robust to external perturbations due to a unique combination of three phenomena: a clock transition, a decoherence-free subspace, and a variant on motional narrowing. The resulting inhomogeneous dephasing time is $T_2^* = 1.9(3)$ minutes, the longest reported for individually controlled qubits. Finally, we develop complete control and realize an entangled state between two spin-pair qubits through projective parity measurements. These long-lived qubits are abundantly present in diamond and other solids, and provide new opportunities for quantum sensing, quantum information processing, and quantum networks.