A Ten-Qubit Solid-State Spin Register with Quantum Memory up to One Minute

Abstract

Spins associated to single defects in solids provide promising qubits for quantum information processing and quantum networks. Recent experiments have demonstrated long coherence times, high-fidelity operations and long-range entanglement. However, control has so far been limited to a few qubits, with entangled states of three spins demonstrated. Realizing larger multi-qubit registers is challenging due to the need for quantum gates that avoid crosstalk and protect the coherence of the complete register. In this paper, we present novel decoherence-protected gates that combine dynamical decoupling of an electron spin with selective phase-controlled driving of nuclear spins. We use these gates to realize a 10-qubit quantum register consisting of the electron spin of a nitrogen-vacancy center and 9 nuclear spins in diamond. We show that the register is fully connected by generating entanglement between all 45 possible qubit pairs, and realize genuine multipartite entangled states with up to 7 qubits. Finally, we investigate the register as a multi-qubit memory. We show coherence times up to 63(2) seconds -the longest reported for a single solid-state qubit -and demonstrate that two-qubit entangled states can be stored for over 10 seconds. Our results enable the control of large quantum registers with long coherence times and therefore open the door to advanced quantum algorithms and quantum networks with solid-state spin qubits.

Towards Large-Scale Quantum Networks

“…3. This platform is a few (about 10 [6]) qubit quantum computer with an optical interface capable of executing arbitrary gates and measurements. It has been recently demonstrated that NV centres are capable of memory lifetimes approaching one minute [6] in nodes not yet interfaced to the network.…”

“…This platform is a few (about 10 [6]) qubit quantum computer with an optical interface capable of executing arbitrary gates and measurements. It has been recently demonstrated that NV centres are capable of memory lifetimes approaching one minute [6] in nodes not yet interfaced to the network. Other platforms exist that are similar on the conceptual level with similar capabilities such as ion traps [33] and neutral atoms [49] (see Table 1 for current parameter trade-offs).…”

Complete Quantum-State Tomography with a Local Random Field

“…The part H N thereby only entails an energy shift A N /2π = ±2. 16 MHz of the electronic m s = ±1 states due to the hyperfine interaction [33,49]. The hyperfine tensor A, on the other hand, describes the dipoledipole interaction between the NV-center electron spin and the carbon nuclear spin.…”

“…While compressed sensing techniques can significantly improve the efficiency of reconstructing low-rank quantum states [2][3][4][5][6][7][8][9][10][11], the problem of identifying an arbitrary state of a complex quantum system with limited measurement access (e.g., to a single qubit only) remains [12][13][14]. For example, one task of practical importance in the development of solid-state quantum devices [15][16][17][18][19] is the complete characterization of coupled spin states. However, when nuclear spins are involved, access to the full system is limited due to their small magnetic moment.…”

Extending qubit coherence by adaptive quantum environment learning

“…However, this technique is limited by the short photo-excited triplet state lifetime, requiring fast polarisation transfer or weakly coupled nuclear spins [32]. A more sophisticated alternative is to use dynamical decoupling sequences to target individual nuclear spins one by one, initialising them in a well defined state [21,23,33]. In addition to improving the coherence of the electron spin, these techniques also enable full coherent control of the individual nuclear spins.…”