The nitrogen-vacancy (NV) centre in diamond is the only solid-state qubit that operates at room temperature, yet its viability for fault-tolerant quantum computing has been dismissed on the grounds that decoherence times are too short. Here we show, through a calibrated twelve-channel decoherence model spanning 1.3 K to 600 K (60+ experimental anchors, R² = 0.953), that single- and two-qubit gate error rates fall below the surface code threshold of 1% at 295 K for bulk ultra-pure diamond under dynamical decoupling with N ≥ 2048 pi-pulses. The key enabler is the recently demonstrated T₂ = 2T₁ limit (4.34 ms at room temperature), achieved by filtering the spin-lattice Han noise channel above 1 MHz via high-order CPMG. The model now includes ¹³C nuclear spectral diffusion (dominant in ultra-pure bulk at high B-field, validated against Wrachtrup QV=8 at -5.4%) and a magnetic-field-dependent T₁ correction. For standard-grade bulk diamond, we identify a Peltier-cooled sweet spot at 200–270 K that brings all gates below threshold at a cooling cost of ~200 EUR. We further show that the XZZX surface code, exploiting the strongly Z-biased noise of NV circuits (effective bias η_eff ≈ 834 from idle-dominated architecture), reduces the physical qubit overhead by more than 95% compared to the standard surface code. Combined with soft-information decoding using analog photoluminescence counts, this establishes a concrete path from the current QV=8 (Wrachtrup 2026) to QV > 1000. Decoherence is no longer the bottleneck for NV-based quantum computing at room temperature. UK Patent Applications GB2606382.6 and GB2606639.9 cover methods described herein.
The nitrogen-vacancy (NV) centre in diamond is the only solid-state qubit that operates at room temperature, yet its viability for fault-tolerant quantum computing has been dismissed on the grounds that decoherence times are too short. Here we show, through a calibrated twelve-channel decoherence model spanning 1.3 K to 600 K (60+ experimental anchors, R² = 0.953), that single- and two-qubit gate error rates fall below the surface code threshold of 1% at 295 K for bulk ultra-pure diamond under dynamical decoupling with N ≥ 2048 pi-pulses. The key enabler is the recently demonstrated T₂ = 2T₁ limit (4.34 ms at room temperature), achieved by filtering the spin-lattice Han noise channel above 1 MHz via high-order CPMG. The model now includes ¹³C nuclear spectral diffusion (dominant in ultra-pure bulk at high B-field, validated against Wrachtrup QV=8 at -5.4%) and a magnetic-field-dependent T₁ correction. For standard-grade bulk diamond, we identify a Peltier-cooled sweet spot at 200–270 K that brings all gates below threshold at a cooling cost of ~200 EUR. We further show that the XZZX surface code, exploiting the strongly Z-biased noise of NV circuits (effective bias η_eff ≈ 834 from idle-dominated architecture), reduces the physical qubit overhead by more than 95% compared to the standard surface code. Combined with soft-information decoding using analog photoluminescence counts, this establishes a concrete path from the current QV=8 (Wrachtrup 2026) to QV > 1000. Decoherence is no longer the bottleneck for NV-based quantum computing at room temperature. UK Patent Applications GB2606382.6 and GB2606639.9 cover methods described herein.
We present NVSim v3.0, a multi-channel decoherence simulator extended from a single-defect NV tool to a unified multi-platform engine covering four color center families: NV⁻ in diamond, VB⁻ in hBN, VSi in 4H-SiC, and PL6 in 4H-SiC. The simulator implements a temperature-dependent model spanning 4–400 K across twelve decoherence channels, including P1 spectral diffusion (Park CCE 2025) with a finite-volume cutoff for nanodiamonds, motional narrowing of the P1 bath at room temperature, ¹³C nuclear spectral diffusion (Maze/Zhao), a magnetic-field-dependent T₁ correction, and a spin-lattice dephasing channel (Han 2025) that quantitatively explains the long-standing empirical limit T₂ ≈ (5/6)T₁. The T₁ model uses the Cambria PRL 2023 two-mode phonon parameterisation, replacing the earlier Jarmola approximation. We validate the model against 60+ experimental anchor points spanning five decades of coherence times, including Herbschleb (bulk, -4.6%), Wrachtrup QV=8 (bulk, -5.4%), and Zvi (nanodiamond, +1.1%), yielding R² = 0.953 with zero post-calibration fitting. Cross-platform comparison reveals qualitatively distinct decoherence landscapes. Temperature scans identify an intermediate-temperature plateau near 250 K accessible via thermoelectric cooling, a diffusion wall at room temperature, and a liquid-nitrogen plateau. NVSim v3.0 constitutes the first multi-defect quantum sensor design platform with quantitative experimental validation across both nanodiamond and bulk diamond regimes.
At its most fundamental level, circuit-based quantum computation relies on the application of controlled phase shift operations on quantum registers. While these operations are generally compromised by noise and imperfections, quantum gates based on geometric phase shifts can provide intrinsically fault-tolerant quantum computing. Here we demonstrate the high-fidelity realization of a recently proposed fast (non-adiabatic) and universal (non-Abelian) holonomic single-qubit gate, using an individual solid-state spin qubit under ambient conditions. This fault-tolerant quantum gate provides an elegant means for achieving the fidelity threshold indispensable for implementing quantum error correction protocols. Since we employ a spin qubit associated with a nitrogen-vacancy colour centre in diamond, this system is based on integrable and scalable hardware exhibiting strong analogy to current silicon technology. This quantum gate realization is a promising step towards viable, fault-tolerant quantum computing under ambient conditions. Quantum gates based on geometric phase shifts offer a promising approach for the realization of fault-tolerant quantum computing. Using nitrogen-vacancy centre qubits in diamond, this study experimentally realises a high-fidelty, non-adiabatic, non-Abelian holonomic single-qubit gate at room temperature.
Preprint — We resolve the long-standing discrepancy between nanodiamond and bulk diamond NV-centre decoherence within a single 12-channel analytical model. Two mechanisms are identified: (1) a finite-volume cutoff that suppresses P1 spectral diffusion in nanodiamonds below ~50 nm, where fewer than 10 P1 atoms prevent thermodynamic bath formation; (2) motional narrowing from P1 Jahn-Teller relaxation (T₁,P1 ≈ 250 µs at RT, τ_ff ≈ 18 ms at 1 ppm) reducing the spectral diffusion rate by 8.5× at room temperature. Validated against 60+ experimental anchors (R² = 0.953) spanning five decades of coherence times, including Zvi (+1.1%), Herbschleb (-4.6%), and Wrachtrup QV=8 (-5.4%) with zero post-calibration fitting.
Abstract Diamond quantum processors consisting of a nitrogen-vacancy centre and surrounding nuclear spins have been the key to significant advancements in room-temperature quantum computing, quantum sensing and microscopy. The optimisation of these processors is crucial for the development of large-scale diamond quantum computers and the next generation of enhanced quantum sensors and microscopes. Here, we present a full model of multi-qubit diamond quantum processors and develop a semi-analytical method for designing gate pulses. This method optimises gate speed and fidelity in the presence of random control errors and is readily compatible with feedback optimisation routines. We theoretically demonstrate infidelities approaching ∼10−5 for single-qubit gates and established evidence that this can also be achieved for a two-qubit CZ gate. Consequently, our method reduces the effects of control errors below the errors introduced by hyperfine field misalignment and the unavoidable decoherence that is intrinsic to the processors. Having developed this optimal control, we simulated the performance of a diamond quantum processor by computing quantum Fourier transforms. We find that the simulated diamond quantum processor is able to achieve fast operations with low error probability.
Nitrogen vacancy (NV-) color centers in diamond are a prime candidate for use in quantum information devices, owing to their spin-1 ground state, straightforward optical initialization and readout, and long intrinsic coherence times in a room-temperature solid. While the 13C nuclear spin is often a dominant source of magnetic noise, we observe transitions between electron-nuclear hyperfine states of NV- centers in 99% 13C diamond that are robust to decoherence. At magnetic field strengths ranging from 550 - 900 G, these transitions are observable by optically detected magnetic resonance (ODMR), and exhibit linewidths narrowed by factors as high as ~130 at room temperature over typical electron-type transitions observed from this spin system. We anticipate the use of these decoherence-protected transitions, in combination with dynamical decoupling methods, for storage of quantum information.
For quantum computers to reach their full potential will require error correction. We study the surface code, one of the most promising quantum error correcting codes, in the context of predominantly dephasing (Z-biased) noise, as found in many quantum architectures. We find that the surface code is highly resilient to Y-biased noise, and tailor it to Z-biased noise, whilst retaining its practical features. We demonstrate ultrahigh thresholds for the tailored surface code: ~39% with a realistic bias of = 100, and ~50% with pure Z noise, far exceeding known thresholds for the standard surface code: ~11% with pure Z noise, and ~19% with depolarizing noise. Furthermore, we provide strong evidence that the threshold of the tailored surface code tracks the hashing bound for all biases. We reveal the hidden structure of the tailored surface code with pure Z noise that is responsible for these ultrahigh thresholds. As a consequence, we prove that its threshold with pure Z noise is 50%, and we show that its distance to Z errors, and the number of failure modes, can be tuned by modifying its boundary. For codes with appropriately modified boundaries, the distance to Z errors is O(n) compared to O(n1/2) for square codes, where n is the number of physical qubits. We demonstrate that these characteristics yield a significant improvement in logical error rate with pure Z and Z-biased noise. Finally, we introduce an efficient approach to decoding that exploits code symmetries with respect to a given noise model, and extends readily to the fault-tolerant context, where measurements are unreliable. We use this approach to define a decoder for the tailored surface code with Z-biased noise. Although the decoder is suboptimal, we observe exceptionally high fault-tolerant thresholds of ~5% with bias = 100 and exceeding 6% with pure Z noise. Our results open up many avenues of research and, recent developments in bias-preserving gates, highlight their direct relevance to experiment.