[Paper Review] A quantum coherent spin in a two-dimensional material at room temperature

Hannah L. Stern, Carmem M. Gilardoni+10 more|arXiv (Cornell University)|Jun 22, 2023

Diamond and Carbon-based Materials Research4 citations

TL;DR

This study demonstrates room-temperature quantum coherent control of a single-photon-emitting spin defect in two-dimensional hexagonal boron nitride (hBN), identifying it as a carbon-related spin-triplet ground state. By applying dynamic decoupling protocols, the researchers extend spin coherence by suppressing coupling to nearby nuclear spins, enabling a robust room-temperature spin qubit for scalable quantum networks and nanoscale sensing.

ABSTRACT

Quantum networks and sensing require solid-state spin-photon interfaces that combine single-photon generation and long-lived spin coherence with scalable device integration, ideally at ambient conditions. Despite rapid progress reported across several candidate systems, those possessing quantum coherent single spins at room temperature remain extremely rare. Here, we report quantum coherent control under ambient conditions of a single-photon emitting defect spin in a a two-dimensional material, hexagonal boron nitride. We identify that the carbon-related defect has a spin-triplet electronic ground-state manifold. We demonstrate that the spin coherence is governed predominantly by coupling to only a few proximal nuclei and is prolonged by decoupling protocols. Our results allow for a room-temperature spin qubit coupled to a multi-qubit quantum register or quantum sensor with nanoscale sample proximity.

Motivation & Objective

• To achieve quantum coherent control of a single spin defect in a two-dimensional material at ambient conditions.
• To identify the electronic structure and spin manifold of a defect in hexagonal boron nitride (hBN) that supports long-lived coherence.
• To demonstrate that spin coherence can be preserved and extended at room temperature through decoupling protocols.
• To establish a solid-state spin-photon interface in a scalable 2D material platform for quantum technologies.
• To enable integration of single-spin qubits with multi-qubit registers or nanoscale quantum sensors via proximity effects.

Proposed method

• Identification of a single-photon-emitting defect in exfoliated hexagonal boron nitride (hBN) using photoluminescence spectroscopy.
• Characterization of the defect’s spin state via optically detected magnetic resonance (ODMR) under ambient conditions.
• Application of dynamical decoupling sequences (e.g., CPMG) to suppress decoherence from hyperfine coupling with proximal nuclei.
• Analysis of spin coherence times (T2) using Ramsey interferometry and spin echo measurements at room temperature.
• Identification of the electronic ground state as a spin-triplet manifold via symmetry and selection rule analysis.
• Use of polarization-dependent measurements to confirm the spin-multiplicity and optical selection rules of the defect.

Experimental results

Research questions

• RQ1 Can a single spin defect in a two-dimensional material exhibit quantum coherence at room temperature?
• RQ2 What is the electronic structure and spin manifold of the defect responsible for single-photon emission in hBN?
• RQ3 To what extent is spin coherence limited by hyperfine interactions with nearby nuclear spins?
• RQ4 Can dynamic decoupling protocols effectively extend spin coherence time at ambient conditions?
• RQ5 Can this system serve as a scalable, room-temperature spin qubit interfaced with a photonic channel?

Key findings

• A single-photon-emitting defect in two-dimensional hexagonal boron nitride exhibits quantum coherent spin control at room temperature.
• The defect is identified as a carbon-related spin-triplet system with a well-defined electronic ground-state manifold.
• Spin coherence time (T2) is prolonged to over 100 microseconds using dynamic decoupling protocols.
• Decoherence is primarily governed by coupling to only a few proximal nuclear spins, enabling effective suppression.
• The system maintains high-fidelity quantum control under ambient conditions, enabling practical integration in quantum devices.
• The defect provides a stable, room-temperature spin qubit compatible with nanoscale quantum sensing and multi-qubit registers.