© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

arXiv:2103.07961 · Physical Review X

Entanglement of Spin-Pair Qubits with Intrinsic Dephasing Times Exceeding a Minute

Hans P. Bartling, M. H. Abobeih, Benjamin Pingault, Maarten J. Degen, S. J. H. Loenen, C. E. Bradley, J. Randall, Matthew Markham, Daniel J. Twitchen, T. H. Taminiau

Published Mar 14, 2022• 56 citations

Abstract

Understanding and protecting the coherence of individual quantum systems is a central challenge in quantum science and technology.Over the past 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 qubits.We study three carbon-13 pairs in diamond and realize high-fidelity measurements of their quantum states using a single nitrogen-vacancy center in their vicinity.We then reveal that the spin pairs are robust to external perturbations due to a combination of three phenomena: a decoherence-free subspace, a clock transition, and a variant on motional narrowing.The resulting inhomogeneous dephasing time is T Ã 2 ¼ 1.9ð3Þ min, the longest reported for individually controlled qubits.Finally, we develop complete control and realize an entangled state between two spin pairs through projective parity measurements.These long-lived qubits are abundantly present in diamond and other solids and provide new opportunities for ancilla-enhanced quantum sensing and for robust memory qubits for quantum networks.

DOI: 10.1103/physrevx.12.011048

Related papers

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

C. E. Bradley, J. Randall, M. H. Abobeih +6 more

Spins associated with single defects in solids provide promising qubits for quantum-information processing and quantum networks.Recent experiments have demonstrated long coherence times, highfidelity 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 multiqubit registers is challenging due to the need for quantum gates that avoid cross talk 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 ten-qubit quantum register consisting of the electron spin of a nitrogen-vacancy center and nine 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 seven qubits.Finally, we investigate the register as a multiqubit memory.We demonstrate the protection of an arbitrary single-qubit state for over 75 s-the longest reported for a single solid-state qubit-and show that two-qubit entanglement can be preserved for over 10 s.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.

arXiv:1905.02094•Physical Review X•Sep 11, 2019•545 citations

Robust Quantum-Network Memory Using Decoherence-Protected Subspaces of Nuclear Spins

Andreas Reiserer, Norbert Kalb, Machiel Blok +5 more

The realization of a network of quantum registers is an outstanding challenge in quantum science and technology.We experimentally investigate a network node that consists of a single nitrogen-vacancy center electronic spin hyperfine coupled to nearby nuclear spins.We demonstrate individual control and readout of five nuclear spin qubits within one node.We then characterize the storage of quantum superpositions in individual nuclear spins under repeated application of a probabilistic optical internode entangling protocol.We find that the storage fidelity is limited by dephasing during the electronic spin reset after failed attempts.By encoding quantum states into a decoherence-protected subspace of two nuclear spins, we show that quantum coherence can be maintained for over 1000 repetitions of the remote entangling protocol.These results and insights pave the way towards remote entanglement purification and the realization of a quantum repeater using nitrogen-vacancy center quantum-network nodes.

arXiv:1603.01602•Physical Review X•Jun 22, 2016•159 citations

Room-Temperature Quantum Bit Memory Exceeding One Second

Peter C. Maurer, Georg Kucsko, Christian Latta +10 more

Stable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. We demonstrate high-fidelity control of a solid-state qubit, which preserves its polarization for several minutes and features coherence lifetimes exceeding 1 second at room temperature. The qubit consists of a single (13)C nuclear spin in the vicinity of a nitrogen-vacancy color center within an isotopically purified diamond crystal. The long qubit memory time was achieved via a technique involving dissipative decoupling of the single nuclear spin from its local environment. The versatility, robustness, and potential scalability of this system may allow for new applications in quantum information science.

Science•Jun 7, 2012•880 citations

Decoherence-protected quantum register of nuclear spins in diamond

F.J. Gonzalez, Raúl Coto

Abstract Solid-state quantum registers are exceptional for storing quantum information at room temperature with long coherence time. Nevertheless, practical applications toward quantum supremacy require even longer coherence time to allow for more complex algorithms. In this work we propose a quantum register that lies in a decoherence-protected subspace to be implemented with nuclear spins nearby a nitrogen-vacancy center in diamond. The quantum information is encoded in two logical states composed of two carbon-13 nuclear spins, while an electron spin is used as ancilla for initialization and control. Moreover, by tuning an off-axis magnetic field we enable non-nuclear-spin-preserving transitions that we use for preparing and manipulating the register through stimulating Raman adiabatic passage. Furthermore, we consider more elaborated sequences to improve simultaneous control over the system yielding decreased gate time.

arXiv:2104.09666•Quantum Science and Technology•Jan 10, 2022•11 citations

Fidelity of remotely entangled nuclear spin states in photon-connected multiqubit registers

Wolf-Rüdiger Hannes, Regina Finsterhoelzl, Guido Burkard

The electron spin of a nitrogen-vacancy center in diamond lends itself to the control of proximal $^{13}\mathrm{C}$ nuclear spins via dynamical decoupling methods, possibly combined with radio-frequency driving. Long-lived single-qubit states and high-fidelity electron-nuclear gates required for the realization of a multiqubit register have already been demonstrated. Towards the goal of a scalable architecture, linking multiple such registers in a photonic network represents an important step. Multiple pairs of remotely entangled qubits can enable advanced algorithms or error correction protocols. We investigate how a photonic architecture can be extended from the intrinsic nitrogen spin to multiple $^{13}\mathrm{C}$ spins per node. Applying decoherence-protected gates sequentially, we simulate the fidelity of creating multiple pairs of remotely entangled qubits. Even though the currently achieved degree of control of $^{13}\mathrm{C}$ spins might not be sufficient for large-scale devices, the two schemes are compatible in principle. One requirement is the correction of unconditional phases acquired by unaddressed nuclear spins during a decoupling sequence.

arXiv:2401.06705•Physical Review A•Nov 26, 2024•5 citations

Room-temperature storage of quantum entanglement using decoherence-free subspace in a solid-state spin system

Fei Wang, Yufei Huang, Zhuo Zhang +8 more

We experimentally demonstrate room-temperature storage of quantum entanglement using two nuclear spins weakly coupled to the electronic spin carried by a single nitrogen-vacancy center in diamond. We realize universal quantum gate control over the three-qubit spin system and produce entangled states in the decoherence-free subspace of the two nuclear spins. By injecting arbitrary collective noise, we demonstrate that the decoherence-free entangled state has coherence time longer than that of other entangled states by an order of magnitude in our experiment.

arXiv:1706.03313•Physical review. B./Physical review. B•Oct 31, 2017•15 citations

Understanding and protecting the coherence of individual quantum systems is a central challenge in quantum science and technology.Over the past 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 qubits.We study three carbon-13 pairs in diamond and realize high-fidelity measurements of their quantum states using a single nitrogen-vacancy center in their vicinity.We then reveal that the spin pairs are robust to external perturbations due to a combination of three phenomena: a decoherence-free subspace, a clock transition, and a variant on motional narrowing.The resulting inhomogeneous dephasing time is T Ã 2 ¼ 1.9ð3Þ min, the longest reported for individually controlled qubits.Finally, we develop complete control and realize an entangled state between two spin pairs through projective parity measurements.These long-lived qubits are abundantly present in diamond and other solids and provide new opportunities for ancilla-enhanced quantum sensing and for robust memory qubits for quantum networks.

Spins associated with single defects in solids provide promising qubits for quantum-information processing and quantum networks.Recent experiments have demonstrated long coherence times, highfidelity 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 multiqubit registers is challenging due to the need for quantum gates that avoid cross talk 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 ten-qubit quantum register consisting of the electron spin of a nitrogen-vacancy center and nine 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 seven qubits.Finally, we investigate the register as a multiqubit memory.We demonstrate the protection of an arbitrary single-qubit state for over 75 s-the longest reported for a single solid-state qubit-and show that two-qubit entanglement can be preserved for over 10 s.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.

The realization of a network of quantum registers is an outstanding challenge in quantum science and technology.We experimentally investigate a network node that consists of a single nitrogen-vacancy center electronic spin hyperfine coupled to nearby nuclear spins.We demonstrate individual control and readout of five nuclear spin qubits within one node.We then characterize the storage of quantum superpositions in individual nuclear spins under repeated application of a probabilistic optical internode entangling protocol.We find that the storage fidelity is limited by dephasing during the electronic spin reset after failed attempts.By encoding quantum states into a decoherence-protected subspace of two nuclear spins, we show that quantum coherence can be maintained for over 1000 repetitions of the remote entangling protocol.These results and insights pave the way towards remote entanglement purification and the realization of a quantum repeater using nitrogen-vacancy center quantum-network nodes.

Stable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. We demonstrate high-fidelity control of a solid-state qubit, which preserves its polarization for several minutes and features coherence lifetimes exceeding 1 second at room temperature. The qubit consists of a single (13)C nuclear spin in the vicinity of a nitrogen-vacancy color center within an isotopically purified diamond crystal. The long qubit memory time was achieved via a technique involving dissipative decoupling of the single nuclear spin from its local environment. The versatility, robustness, and potential scalability of this system may allow for new applications in quantum information science.

Abstract Solid-state quantum registers are exceptional for storing quantum information at room temperature with long coherence time. Nevertheless, practical applications toward quantum supremacy require even longer coherence time to allow for more complex algorithms. In this work we propose a quantum register that lies in a decoherence-protected subspace to be implemented with nuclear spins nearby a nitrogen-vacancy center in diamond. The quantum information is encoded in two logical states composed of two carbon-13 nuclear spins, while an electron spin is used as ancilla for initialization and control. Moreover, by tuning an off-axis magnetic field we enable non-nuclear-spin-preserving transitions that we use for preparing and manipulating the register through stimulating Raman adiabatic passage. Furthermore, we consider more elaborated sequences to improve simultaneous control over the system yielding decreased gate time.

The electron spin of a nitrogen-vacancy center in diamond lends itself to the control of proximal

^{13}\mathrm{C}

nuclear spins via dynamical decoupling methods, possibly combined with radio-frequency driving. Long-lived single-qubit states and high-fidelity electron-nuclear gates required for the realization of a multiqubit register have already been demonstrated. Towards the goal of a scalable architecture, linking multiple such registers in a photonic network represents an important step. Multiple pairs of remotely entangled qubits can enable advanced algorithms or error correction protocols. We investigate how a photonic architecture can be extended from the intrinsic nitrogen spin to multiple

^{13}\mathrm{C}

spins per node. Applying decoherence-protected gates sequentially, we simulate the fidelity of creating multiple pairs of remotely entangled qubits. Even though the currently achieved degree of control of

^{13}\mathrm{C}

spins might not be sufficient for large-scale devices, the two schemes are compatible in principle. One requirement is the correction of unconditional phases acquired by unaddressed nuclear spins during a decoupling sequence.

We experimentally demonstrate room-temperature storage of quantum entanglement using two nuclear spins weakly coupled to the electronic spin carried by a single nitrogen-vacancy center in diamond. We realize universal quantum gate control over the three-qubit spin system and produce entangled states in the decoherence-free subspace of the two nuclear spins. By injecting arbitrary collective noise, we demonstrate that the decoherence-free entangled state has coherence time longer than that of other entangled states by an order of magnitude in our experiment.