Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins

At a Glance

Metadata	Details
Publication Date	2021-07-20
Journal	Nature Communications
Authors	Michal Gulka, Daniel Wirtitsch, Viktor Ivády, Jelle Vodnik, Jaroslav Hruby
Institutions	Linköping University, Imec the Netherlands
Citations	54
Analysis	Full AI Review Included

Executive Summary

This analysis summarizes the room-temperature control and electrical readout of individual nitrogen-vacancy (NV) nuclear spins in diamond, a critical step toward scalable quantum microelectronics.

Core Achievement: Demonstrated room-temperature control and electrical readout of a single intrinsic ¹⁴N nuclear spin coupled to the NV electron spin in diamond.
Readout Mechanism: Utilizes Photoelectric Detection of Magnetic Resonance (PDMR), where the NV spin state is determined by measuring the photocurrent generated via two-photon ionization.
Scalability Advantage: PDMR readout area is limited by the inter-electrode distance (nanoscale compatibility), not the optical diffraction limit, enabling high-density integration.
Operating Conditions: The device operates at ambient conditions (room temperature) and utilizes the Excited-State Level Anti-Crossing (ESLAC) condition (~510 G) for efficient spin polarization (>98%).
Quantum Gates: Achieved high-contrast detection of nuclear magnetic resonance spectra and coherent nuclear spin Rabi oscillations using pulsed PDMR techniques.
Theoretical Framework: A Lindblad master equation model was developed to describe the spin and photoelectric transitions, providing the necessary theory for designing photoelectric quantum gate operations.
Future Impact: This demonstration is a foundational step toward developing electronic quantum processors based on the dipolar interaction of spin-qubits placed at nanoscopic proximity.

Technical Specifications

Parameter	Value	Unit	Context
Operating Temperature	Ambient	°C	Room-temperature operation of the quantum device.
Diamond Material	IIa HPHT	N/A	Commercial diamond with <10 ppb background nitrogen.
Excitation Wavelength	561	nm	Yellow-green laser used to minimize background current from P1 centers.
Laser Power (Readout)	4-6	mW	Applied to increase NV-generated photocurrent for low average current detection.
Optimal Bias Voltage	8.6	V	Set to achieve maximum NV Signal-to-Background Contrast (SBC).
Maximum NV SBC	>65	%	Contrast achieved at 8.6 V bias.
Magnetic Field (ESLAC)	~510	G	Field required for Excited-State Level Anti-Crossing (ESLAC) operation.
Electrode Gap	3.5	µm	Inter-electrode distance for coplanar contacts fabricated via optical lithography.
Electrical Axial Resolution (FWHM)	0.9	µm	Resolution achieved via PDMR imaging (threefold improvement over optical).
Optical Axial Resolution (FWHM)	2.7	µm	Resolution achieved via standard optical imaging.
Nuclear Spin Polarization	>98	%	Polarization achieved for the ¹⁴N nuclear spin via optical pumping near ESLAC.
MW π-Pulse Duration	400	ns	Used for selective electron spin manipulation (MW0).
Readout Laser Pulse Duration	4000	ns	Used for pulsed PDMR measurements (at 6 mW power).

Key Methodologies

Material Preparation: A commercial IIa high-pressure high-temperature (HPHT) diamond crystal (<10 ppb background nitrogen) containing intrinsic single NV defects was used.
Device Fabrication: Coplanar interdigitated contacts with a 3.5 µm gap were fabricated on the diamond surface using optical lithography to collect charge carriers under bias voltage.
NV Center Selection: Individual NV centers were stochastically allocated between the electrodes and selected if they were located approximately 2.5 µm below the diamond surface.
Excitation Source: A yellow-green 561 nm (2.21 eV) laser was used for excitation, chosen over the common 532 nm green laser to reduce background photocurrent induced by photoionization of substitutional nitrogen (P1 centers).
Readout Technique (PDMR): The spin state was read out electrically by measuring the photocurrent generated by the spin state-dependent two-photon photoionization of the NV center.
Detection Setup: Photocurrent was pre-amplified and recorded using lock-in detection. A pulsed lock-in envelope readout technique was employed, where the lock-in amplifier was triggered by the rising edge of the low-frequency laser envelope.
Spin Polarization and Initialization: The ¹⁴N nuclear spin was polarized to the |m_I) = |+1) state by applying an external magnetic field of ~510 G, aligning it with the NV axis to leverage the spin mixing near the ESLAC.
Coherent Control: Coherent nuclear spin rotations were driven using Radiofrequency (RF) pulses, combined with Microwave (MW)-assisted electron spin readout (using MW π-pulses for selective electron spin swapping).
Theoretical Modeling: The system dynamics were described using the Lindblad master equation, incorporating five electronic states (GS, ES, MS in NV^-; GS, ES in NV⁰) and 13 Lindblad operators to model charge state transitions and spin dynamics.

Commercial Applications

The development of room-temperature, electrically-readout NV nuclear spin qubits has direct relevance to several high-tech sectors:

Quantum Computing: Enables the development of scalable, solid-state quantum processors by overcoming the diffraction limit constraint of optical readout, allowing for dense integration of qubits.
Quantum Sensing: Applicable in high-dynamic-range magnetometry and nanoscale spectroscopy, utilizing the long coherence times of nuclear spins as quantum memories.
Quantum Communication: Provides a robust, room-temperature platform for quantum network nodes and quantum repeaters, potentially enhancing entanglement rates.
Microelectronic Devices: Facilitates the integration of quantum functionalities directly into conventional semiconductor microelectronic chips, leading to hybrid quantum-classical devices.
Diamond Material Engineering: Drives demand for high-purity, low-nitrogen HPHT or CVD diamond substrates optimized for deterministic NV center creation and high charge carrier mobility.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-021-24494-x