| Metadata | Details |
|---|
| Publication Date | 2025-04-11 |
| Journal | Physical Review X |
| Authors | Hans K. C. Beukers, Christopher Waas, M. Pasini, Hendrik B. van Ommen, Zarije Ademi |
| Institutions | Delft University of Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
- Improved Qubit Control: Demonstrated enhanced control over solid-state nuclear spin qubits (specifically 13C) using the electron spin-1/2 system of a diamond Tin-Vacancy (SnV) center.
- DDRF Superiority: Introduced Dynamically Decoupled Radio-Frequency (DDRF) control, which provides intrinsically improved selectivity for spin-1/2 systems compared to standard Dynamical Decoupling (DD) methods.
- Long Coherence: Achieved a long electron spin coherence time (T2DD) of 1.7 ms using XY8 dynamical decoupling sequences, enabling complex, multi-pulse gate operations.
- Dual Nuclear Spin Control: Successfully identified and coherently controlled two distinct 13C nuclear spins (CA and CB), including one (CB) that was undetectable using the conventional DD method.
- High-Fidelity Entanglement: Generated electron-nuclear Bell state entanglement with a state fidelity of 72(3)%, limited primarily by electron coherence loss during the gate sequence.
- Excited State Insights: Employed time-resolved readout to quantify the hyperfine coupling difference between the electronās ground and excited states, crucial for optimizing optical initialization and readout.
| Parameter | Value | Unit | Context |
|---|
| Qubit Host Material | Diamond (CVD grown) | N/A | Natural 13C abundance (1.1%) |
| Implantation Species | 120Sn (spinless) | N/A | Used to create SnV centers |
| Implantation Dose | 5 x 1010 | ions/cm2 | Target depth 88 nm |
| Annealing Temperature | 1100 | Ā°C | Post-implantation processing |
| Operating Temperature | 0.4 | K | He cryostat base temperature |
| Bias Magnetic Field (BDC) | 0.1 | T | Aligned with SnV symmetry axis |
| Optical Excitation Wavelength | 619 | nm | Used for initialization and readout |
| Electron Initialization Fidelity | 98.1(5) | % | Achieved via spin pumping (300 Āµs) |
| Single-Shot Readout Fidelity (Average) | 77.7(3) | % | Optimized readout time |
| Electron Rabi Frequency | 2.46 | MHz | Microwave control |
| Electron Dephasing Time (T2*) | 2.42(4) | Āµs | Measured coherence without DD |
| Electron Coherence Time (T2DD) | 1.7(5) | ms | Using 256 XY8 pulses |
| Nuclear Spin CA Parallel Hyperfine (A||) | -130.9(3) | kHz | Extracted from DD control |
| Nuclear Spin CB Parallel Hyperfine (A||) | 304.45(5) | kHz | Extracted from DDRF control |
| Electron-Nuclear Entanglement Fidelity | 72(3) | % | Bell state (Ī¦+) fidelity |
| Nuclear Spin CB Coherence Time (T2*) | 17.2(6) | ms | Measured via Ramsey sequence |
- Sample Fabrication: Chemical Vapor Deposition (CVD) diamond was implanted with 120Sn ions (5 x 1010 ions/cm2) and subsequently annealed at 1100 Ā°C to create negatively charged Tin-Vacancy (SnV) centers.
- Cryogenic Setup: Experiments were performed in a He cryostat at 0.4 K, utilizing a confocal optical microscope and a 0.1 T bias magnetic field (BDC) aligned with the SnV symmetry axis.
- Electron Qubit Initialization and Readout: The electron spin-1/2 was initialized via spin pumping and read out using spin-selective optical excitation at 619 nm, achieving single-shot readout fidelity of 77.7%.
- Dynamically Decoupled Radio-Frequency (DDRF) Control: Conditional nuclear spin gates were realized by combining direct radio-frequency (rf) driving of the nuclear spin with Dynamical Decoupling (DD) sequences (XY8) on the electron spin for coherence protection.
- Gate Optimization and Spectroscopy: A two-dimensional DDRF spectrum (varying targeted average precession frequency $\tilde{\omega}$ and rf frequency $\omega_{rf}$) was measured to identify and optimize control parameters for specific 13C nuclear spins (CA and CB).
- Entanglement Generation: A Bell state (Ī¦+) was created between the electron spin and the nuclear spin CB using the optimized DDRF gate, preceded by Measurement-Based Initialization (MBI) of the nuclear spin.
- Excited State Hyperfine Analysis: Time-resolved photon detection during MBI readout was used to measure the phase shift acquired by the nuclear spin while the electron was in the excited state, allowing extraction of the difference in parallel hyperfine coupling (ĪA||).
- Quantum Computing (Solid-State Qubits): The SnV center, operating as a high-quality electron spin-1/2 qubit, coupled with long-lived 13C nuclear memories, forms a robust quantum register suitable for scalable, fault-tolerant quantum processors.
- Quantum Networks and Communication: The use of nuclear spins as long-lived quantum memory (T2* up to 17.2 ms) during optical operations is critical for developing multi-node quantum networks and memory-assisted quantum communication protocols.
- High-Selectivity Quantum Sensing: The DDRF control method provides a pathway to enhance the selectivity of quantum sensors based on spin-1/2 systems (e.g., Silicon-Vacancy, Germanium-Vacancy, or Silicon T centers) for high-resolution magnetic and electric field detection.
- Advanced Diamond Material Platforms: The control techniques are directly applicable to other Group-IV color centers in diamond (SiV, GeV, PbV) and other spin-1/2 systems like rare-earth ions, accelerating the development of these platforms.
- Integrated Photonics: The SnV centerās compatibility with nanophotonic integration (as noted in the introduction) supports the development of on-chip quantum devices and integrated quantum circuits.
View Original Abstract
Solid-state quantum registers consisting of optically active electron spins with nearby nuclear spins are promising building blocks for future quantum technologies. For electron spin-1 registers, dynamical decoupling (DD) quantum gates have been developed that enable the precise control of multiple nuclear spin qubits. However, for the important class of electron spin-<a:math xmlns:a=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><a:mrow><a:mn>1</a:mn><a:mo>/</a:mo><a:mn>2</a:mn></a:mrow></a:math> systems, this control method suffers from intrinsic selectivity limitations, resulting in reduced nuclear spin gate fidelities. Here, we demonstrate improved control of single nuclear spins by an electron spin-<c:math xmlns:c=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><c:mrow><c:mn>1</c:mn><c:mo>/</c:mo><c:mn>2</c:mn></c:mrow></c:math> using dynamically decoupled radio-frequency (DDRF) gates. We make use of the electron spin-<e:math xmlns:e=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><e:mrow><e:mn>1</e:mn><e:mo>/</e:mo><e:mn>2</e:mn></e:mrow></e:math> of a diamond tin-vacancy center, showing high-fidelity single-qubit gates, single-shot readout, and spin coherence beyond a millisecond. The DD control is used as a benchmark to observe and control a single <g:math xmlns:g=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><g:mrow><g:mmultiscripts><g:mrow><g:mn>3</g:mn></g:mrow><g:mprescripts/><g:none/><g:mrow><g:mn>1</g:mn></g:mrow></g:mmultiscripts><g:mi mathvariant=ānormalā>C</g:mi></g:mrow></g:math> nuclear spin. Using the DDRF control method, we demonstrate improved control on that spin. In addition, we find and control an additional nuclear spin that is insensitive to the DD control method. Using these DDRF gates, we show entanglement between the electron and the nuclear spin with 72(3)% state fidelity. Our extensive simulations indicate that DDRF gate fidelities well in excess are feasible. Finally, we employ time-resolved photon detection during readout to quantify the hyperfine coupling for the electronās optically excited state. Our work provides key insights into the challenges and opportunities for nuclear spin control in electron spin-<j:math xmlns:j=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><j:mrow><j:mn>1</j:mn><j:mo>/</j:mo><j:mn>2</j:mn></j:mrow></j:math> systems, opening the door to multiqubit experiments on these promising qubit platforms.