Nanotube double quantum dot spin transducer for scalable quantum information processing

At a Glance

Metadata	Details
Publication Date	2020-04-28
Journal	New Journal of Physics
Authors	Wanlu Song, Tianyi Du, Haibin Liu, Ralf Betzholz, Jianming CAI
Citations	2
Analysis	Full AI Review Included

Executive Summary

This research proposes a novel hybrid quantum architecture utilizing a carbon nanotube double quantum dot (DQD) as a spin transducer to achieve scalable, steady-state entanglement between distant Nitrogen-Vacancy (NV) center electron spins in diamond.

Core Value Proposition: Achieves robust, deterministic entanglement between NV centers separated by micrometer distances, overcoming the rapid decay associated with direct dipolar coupling.
Mechanism: Entanglement is generated via the Pauli blockade mechanism in the DQD. The system is driven into a unique dark state where the DQD is blocked in a triplet state (|T₀>) and the NV electron spins are maximally entangled (|Φ^->).
Scalability: The steady-state entanglement of the electron spins is exploited to realize controlled-phase gates between associated ¹⁵N nuclear spins, enabling the generation of scalable 1D and 2D cluster states for measurement-based quantum computation.
Operational Requirements: The scheme requires only voltage control of the nanotubes and microwave driving of the NV electron spins, making it feasible with current state-of-the-art experimental capabilities.
Noise Robustness: The entanglement generation mechanism is highly tolerant to typical solid-state noise, including magnetic field fluctuations (from ¹³C nuclear spins) and electric potential fluctuations (gate voltage noise up to ±1 µeV).
Performance: Optimal entanglement preparation time (t_c) is achieved in approximately 45 µs under optimized tunneling and driving rates.

Technical Specifications

Parameter	Value	Unit	Context
NV-Center Separation	Up to micrometers	µm	Distance over which entanglement is mediated.
Optimal Entanglement Time (t_c)	45	µs	Time required to prepare the maximally entangled state.
Optimal Tunneling Rate (J/2π)	24	MHz	Inter-dot tunneling rate for optimized performance.
Optimal Rabi Frequency (Ω/2π)	0.6	MHz	Microwave driving frequency for NV electron spins.
Electron Transport Rate (Γ_in = Γ_out)	0.5	GHz	Injection and ejection rates for the DQD cycle (ideal case).
External Magnetic Field (B_z)	5	mT	Applied field used to lift spin sublevel degeneracy.
¹⁵N Hyperfine Coupling (A_\|\|/2π)	3.03	MHz	Coupling strength used for nuclear-spin gate implementation.
DQD Tunneling Rate (J) Max	100	MHz	Achievable rate for an inter-dot distance of 1 µm [47].
Electric Noise Tolerance (Δ)	±1	µeV	Tolerance range for energy difference between singlet states (S and S_g).
NV Zero-Field Splitting (D/2π)	2.87	GHz	Ground state splitting of the NV electron spin.
Magnetic Noise Tolerance (√v)	50 to 150	kHz	Range of magnetic field fluctuation variance tested.

Key Methodologies

The proposed architecture relies on quantum transport and spin-valley blockade mechanisms within a hybrid solid-state system:

Hybrid System Assembly: Single NV centers embedded in diamond nanopillars are placed above a carbon nanotube bridging source and drain contacts. Electrostatic gates define the DQD within the nanotube.
Qubit Definition: The NV electron spin sublevels (|m_s = +1> and |m_s = -1>) encode the primary qubit. The DQD utilizes valley-spin qubits formed by Kramers doublets.
Electron Transport Cycle: Under a large bias voltage, electrons cycle through the DQD via the sequence (0,1) ↔ (1,1) ↔ (0,2) → (0,1), where (n_L, n_R) denotes the electron count in the left and right dots.
Pauli Blockade Implementation: The (1,1) → (0,2) transition is forbidden by the Pauli exclusion principle if the two electrons in the (1,1) configuration occupy specific triplet states, notably |T₀>. This blockade is robust against electric noise.
Spin Transduction: Magnetic dipole-dipole coupling (κ) links the NV electron spins to the DQD valley spins. This coupling, combined with microwave driving (Ω) of the NV spins, selectively couples all states except the target dark state.
Steady-State Preparation: The system dynamically evolves into the unique decoupled dark state, which is the product state |T₀> ⊗ |Φ^->. This prepares the NV electron spins into the maximally entangled Bell state |Φ^->.
Scalable Gate Implementation: The electron spin entanglement is transferred to the highly coherent ¹⁵N nuclear spins via hyperfine coupling (A_||), enabling the realization of a controlled-phase gate, a necessary component for universal measurement-based quantum computation.
Noise Mitigation Techniques: To maintain coherence, the scheme relies on isotopically engineered diamond and dynamical decoupling techniques to suppress magnetic field noise, and optimization of transport rates (Γ_in, Γ_out) and tunneling (J) to compensate for electric potential fluctuations (Δ).

Commercial Applications

This technology provides a fundamental building block for scalable quantum architectures, impacting several high-tech sectors:

Quantum Computing Hardware:
- Development of scalable solid-state quantum processors based on hybrid NV-DQD platforms.
- Resource generation for measurement-based quantum computation (MBQC) through the creation of 1D and 2D nuclear-spin cluster states.
Quantum Communication and Networking:
- Deterministic generation of entanglement between distant quantum nodes, crucial for long-range quantum networks.
Advanced Quantum Sensing:
- Utilizes high-coherence NV centers, which are key components in nanoscale magnetometry, electric field sensing, and thermometry.
Carbon Nanomaterial Engineering:
- Requires high-precision fabrication and control of carbon nanotube DQDs, including isotopically purified nanotubes for enhanced coherence.
Hybrid Device Integration:
- Pioneering the integration of solid-state defects (NV centers) with semiconductor quantum structures (nanotubes) for robust quantum control.

View Original Abstract

Abstract One of the key challenges for the implementation of scalable quantum information processing is the design of scalable architectures that support coherent interaction and entanglement generation between distant quantum systems. We propose a nanotube double quantum dot spin transducer that allows to achieve steady-state entanglement between nitrogen-vacancy center spins in diamond with spatial separations up to micrometers. The distant spin entanglement further enables us to design a scalable architecture for solid-state quantum information processing based on a hybrid platform consisting of nitrogen-vacancy centers and carbon-nanotube double quantum dots.

Tech Support

Original Source

DOI: https://doi.org/10.1088/1367-2630/ab8e16

References

2010 - Quantum computers [Crossref]
2011 - Natural and artificial atoms for quantum computation [Crossref]
2007 - Linear optical quantum computing with photonic qubits [Crossref]
2008 - Quantum coherence and entanglement with ultracold atoms in optical lattices [Crossref]
2008 - Entangled states of trapped atomic ions [Crossref]
2008 - Superconducting quantum bits [Crossref]
1998 - Quantum computation with quantum dots [Crossref]
2007 - Spins in few-electron quantum dots [Crossref]
2008 - Coherent manipulation of single spins in semiconductors [Crossref]
2009 - Hybrid quantum devices and quantum engineering [Crossref]