[Paper Review] Single-shot readout of multiple nuclear spin qubits in diamond under ambient conditions

A. Dréau, Piernicola Spinicelli+3 more|arXiv (Cornell University)|Oct 23, 2012

Diamond and Carbon-based Materials Research3 citations

TL;DR

This paper demonstrates single-shot, high-fidelity readout of multiple nuclear spin qubits in diamond at room temperature using a nitrogen-vacancy (NV) defect's electronic spin as a quantum sensor. By leveraging hyperfine interactions and optical initialization, the authors achieve simultaneous readout of a 13C nuclear spin and the NV's intrinsic 14N nuclear spin, with polarization lifetimes exceeding seconds, enabling scalable quantum information processing under ambient conditions.

ABSTRACT

We use the electronic spin of a single Nitrogen-Vacancy (NV) defect in diamond to observe the real-time evolution of neighboring single nuclear spins under ambient conditions. Using a diamond sample with a natural abundance of $^{13}$C isotopes, we first demonstrate high fidelity initialization and single-shot readout of an individual $^{13}$C nuclear spin. By including the intrinsic $^{14}$N nuclear spin of the NV defect in the quantum register, we then report the simultaneous observation of quantum jumps linked to both nuclear spin species, providing an efficient initialization of the two qubits. These results open up new avenues for diamond-based quantum information processing including active feedback in quantum error correction protocols and tests of quantum correlations with solid-state single spins at room temperature.

Motivation & Objective

• To achieve high-fidelity, single-shot readout of individual 13C nuclear spins in diamond under ambient conditions.
• To demonstrate simultaneous initialization and readout of two nuclear spin qubits: 13C and the NV defect's intrinsic 14N nuclear spin.
• To enable robust quantum information processing by extending coherence times and improving initialization fidelity using optical and microwave control.
• To explore the feasibility of active feedback and quantum error correction in solid-state systems at room temperature.

Proposed method

• Utilizes the electronic spin of a nitrogen-vacancy (NV) defect in diamond as a quantum sensor to detect and control nearby nuclear spins via hyperfine interactions.
• Employs pulsed microwave and optical excitation to coherently manipulate and read out the NV electronic spin state, which is entangled with the nuclear spins.
• Applies a static magnetic field along the NV axis to tune level anti-crossings and enhance spin readout fidelity through optical detection of electron spin resonance (OD-ESR).
• Uses a two-state Hidden Markov Model to analyze photoluminescence time traces and extract nuclear spin relaxation times (T1) from quantum jump statistics.
• Models depolarization rates using hyperfine coupling components: anisotropic (Aani), longitudinal (Azz), and transverse (A⊥), with rates dependent on magnetic field strength.
• Fits experimental T1 data using a weighted sum of depolarization rates (γ1 ≈ αaniγani + α⊥(gs)γ⊥(gs) + α⊥(es)γ⊥(es)) to reproduce field-dependent relaxation trends.

Experimental results

Research questions

• RQ1 Can single-shot, high-fidelity readout of a 13C nuclear spin be achieved in natural-abundance diamond at room temperature?
• RQ2 Can the intrinsic 14N nuclear spin of the NV defect be coherently used as a qubit in a multi-qubit register with a 13C nuclear spin?
• RQ3 What are the dominant decoherence mechanisms affecting nuclear spin relaxation in the presence of hyperfine coupling and external magnetic fields?
• RQ4 How does the magnetic field orientation influence the depolarization rate and coherence time of nuclear spins?

Key findings

• High-fidelity single-shot readout of a 13C nuclear spin is achieved with a polarization lifetime exceeding seconds at moderate magnetic fields.
• The intrinsic 14N nuclear spin of the NV defect enables efficient two-qubit initialization, allowing simultaneous observation of quantum jumps in both 13C and 14N spin states.
• The 13C hyperfine interaction strength is measured as Azz = 258 ± 10 kHz, confirming strong coupling to the NV electronic spin.
• Depolarization is dominated by the anisotropic hyperfine component (Aani), with a significant rate even at 1 kHz, except near level anti-crossings.
• Relaxation times T1 for the 13C spin show strong magnetic field dependence, with the bright state (|0⟩e|↑⟩) exhibiting longer T1 than the dark state (|−1⟩e|↓⟩).
• A simplified model using weighted depolarization rates reproduces the experimental T1 trend across magnetic fields, validating the role of hyperfine coupling in relaxation dynamics.