Quantum Computing Breakthrough: Individual Nuclear Spins Achieve Record Coherence Times

Revolutionary Nuclear Spin Qubits Shatter Coherence Records

In a landmark development published in Nature Physics, researchers have demonstrated individual solid-state nuclear spin qubits maintaining coherence for over one second—a monumental achievement that pushes the boundaries of quantum computing hardware. This breakthrough represents more than an order of magnitude improvement over previous records and establishes nuclear spins as serious contenders for scalable quantum information processing.

The experimental system utilizes erbium electron spins coupled to tungsten nuclear spins in a calcium tungstate crystal. What makes this platform particularly remarkable is that these record coherence times were achieved in natural-abundance materials, without requiring expensive isotopic purification that has been necessary in other quantum computing approaches., according to industry developments

Overcoming Technical Hurdles with Innovative Control Methods

The research team faced significant technical challenges in controlling nuclear spins directly. Traditional radio-frequency driving was impossible due to the superconducting resonator’s suppression of low-frequency fields. Instead, the researchers developed an ingenious approach using sideband transitions that simultaneously flip both electron and nuclear spins., as earlier coverage

This method leverages the hyperfine interaction between electron and nuclear spins, specifically the zx terms in the Hamiltonian that make these transitions weakly allowed. By driving red and blue sideband transitions with repeated chirped pulses, the system can be pumped into specific nuclear spin states with high fidelity., according to further reading

Quantum Non-Demolition Readout Enables High-Fidelity Measurement

The detection scheme represents another engineering triumph. Researchers excite the electron spin at four distinct frequencies corresponding to different nuclear spin configurations and detect emitted photons. The bandwidths of the resonator and single-molecule photon detector—640 kHz and approximately 200 kHz respectively—prove sufficient to span all transition frequencies simultaneously., according to recent developments

This approach enables quantum non-demolition (QND) readout, where measuring the nuclear spin state doesn’t destroy the quantum information. The system achieves impressive readout fidelities of 0.91 to 0.95 for different nuclear spin states, limited mainly by state preparation errors and minor cross-relaxation effects during measurement.

Stimulated Raman Transitions: The Key to Coherent Control

Perhaps the most significant innovation lies in the use of stimulated Raman transitions for coherent control. By applying two simultaneous microwave tones at different frequencies, researchers can drive nuclear spin transitions without populating the electron spin excited state.

This technique offers several crucial advantages:

• Immunity to electron spin decoherence: Since the electron spin remains in its ground state, its relatively short coherence time doesn’t affect nuclear spin operations
• All-microwave operation: Eliminates the need for challenging radio-frequency controls
• High-fidelity gates: Enables precise single- and two-qubit operations

Record-Breaking Coherence Times and Future Implications

The coherence measurements reveal extraordinary performance. Ramsey experiments show free-induction decay times of 0.8 seconds for one qubit and 1.2 seconds for the other—surpassing previous records by more than an order of magnitude. Even more impressively, Hahn echo measurements extend these coherence times to 3.4 and 4.4 seconds respectively.

These timescales are competitive with those achieved in isotopically enriched silicon and diamond systems, suggesting that CaWO₄ could become a leading platform for spin-based quantum computing. The researchers note that coherence is likely limited by magnetic field drift and spectral diffusion from the nuclear spin bath, suggesting even longer times might be achievable with improved experimental conditions.

Industrial Applications and Future Directions

This breakthrough has significant implications for quantum computing development. The combination of long coherence times, high-fidelity readout, and all-microwave control makes this platform particularly attractive for scalable quantum processor architectures.

Potential applications extend beyond quantum computing to quantum sensing and quantum networks. The exceptional coherence times could enable ultra-sensitive magnetometers or quantum memories for long-distance quantum communication.

Looking forward, the researchers suggest that dynamically detuning the resonator from the erbium spin during pulse sequences, combined with advanced dynamical decoupling techniques, could further extend coherence times. This research establishes nuclear spins in solid-state systems as a viable path toward practical quantum technologies, potentially accelerating the timeline for fault-tolerant quantum computation.

The demonstrated capabilities position nuclear spin qubits as serious competitors in the race to build practical quantum computers, offering a unique combination of long coherence, precise controllability, and measurement fidelity that could transform the quantum computing landscape.

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