One-step implementation of a hybrid Fredkin gate with quantum memories and single superconducting qubit in circuit QED and its applications
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-02-12 |
| Journal | Optics Express |
| Authors | Tong Liu, Bao-qing Guo, Changâshui Yu, WeiâNing Zhang |
| Institutions | Dalian University of Technology |
| Citations | 48 |
| Analysis | Full AI Review Included |
Hybrid Fredkin Gate Implementation Using Circuit QED and Solid-State Quantum Memories
Section titled âHybrid Fredkin Gate Implementation Using Circuit QED and Solid-State Quantum MemoriesâTechnical Documentation and Material Solutions provided by 6CCVD (6ccvd.com)
Executive Summary
Section titled âExecutive SummaryâThis documentation analyzes the feasibility of implementing a hybrid Fredkin (controlled-SWAP) gate using a superconducting flux qubit coupled to solid-state quantum memories within a circuit Quantum Electrodynamics (cQED) architecture. The proposed scheme simplifies multi-qubit gate construction and reduces decoherence by utilizing long-coherence materials, which directly aligns with 6CCVDâs advanced MPCVD Single Crystal Diamond (SCD) capabilities.
- Core Achievement: Proposed a direct, single-step realization of a general hybrid tripartite Fredkin gate, significantly simplifying the operation compared to multi-step gate sequences.
- Architecture: Hybrid system utilizing a superconducting flux qubit (control) coupled to two quantum memories (target qudits).
- Material Flexibility: Memories can be superconducting resonators or Nitrogen-Vacancy (NV) center ensembles in diamond.
- Coherence Advantage: Leverages materials with long coherence times (up to 1 second reported for NV ensembles) to maintain state integrity.
- High Fidelity Demonstrated: Numerical simulations predict high fidelity (up to 98.5%) for generating complex entangled states (NOON, Entangled Coherent, and Cat states).
- Critical Material Requirement: Successful implementation, especially involving solid-state memories, depends critically on ultra-high-purity Single Crystal Diamond (SCD) substrates for NV ensemble integration and low-loss cQED fabrication.
- Application Potential: The gate enables the efficient generation of arbitrary entangled states and direct measurement of fidelity and entanglement between quantum memories.
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters were extracted from the theoretical proposal and numerical simulations, highlighting the demanding requirements for system components, particularly in coherence and coupling strength.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Flux Qubit T1 (Level | a | ) | 2 |
| Flux Qubit T1 (Level | e | ) | 5 |
| Flux Qubit T2* (Dephasing) | 5 | ”s | Conservative dephasing time used in simulation. |
| Memory Lifetime (Îș-1) | 5 | ”s | Conservative estimate for resonator/NV ensemble lifetime. |
| Reported NV Ensemble Lifetime | 1 | s | State-of-the-art result referenced (Ref 29). |
| Coupling Constant (g/2Ï) | 70 | MHz | Resonator-qubit or NV-qubit coupling used in simulation. |
| Rabi Frequency (Ω/2Ï) | 100 | MHz | Attainable experimental value for qubit control. |
| NV Center Zero-Field Splitting | â 2.878 | GHz | Energy gap between |
| Max Entangled Coherent State Fidelity | 98.5 | % | Achieved at detuning ratio D = 10. |
| Max NOON State Fidelity | 96.0 | % | Achieved at detuning ratio D = 16. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment proposes a simplified, efficient approach to implementing a complex three-qubit gate by leveraging strong coupling and large detuning in cQED systems.
- Architecture: The core system consists of a three-level superconducting flux qutrit (coupler) acting as the control qubit, dispersively coupled via capacitors (C1, C2) to two quantum memories (Resonator 1, Resonator 2).
- Quantum Memory Options: The target qudits are realized either through:
- Superconducting coplanar waveguide resonators (high coherence, high-Q).
- Nitrogen-Vacancy (NV) center ensembles embedded in high-purity diamond.
- Hamiltonian Simplification: By ensuring the resonators are far-off resonant from the qubit transition (|g> â |a>), the system operates under large-detuning conditions (ÎŽ1 >> g1 and ÎŽ2 >> g2).
- Single-Step Unitary Operation: The large detuning allows the effective Hamiltonian to simplify into a form (He = H0 + Hi) that enables the Fredkin gate to be realized using a single unitary operation over a time T = Ï/(2λ), without requiring multiple microwave pulses.
- Entanglement Generation: Entangled states (NOON, Coherent, Cat states) are generated by applying a single microwave pulse resonant with the qubit transition (|g> â |e>) and performing a subsequent von Neumann measurement on the flux qubit.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful implementation of hybrid quantum circuits integrating solid-state memories (NV ensembles) with cQED relies fundamentally on ultra-high-quality diamond material that 6CCVD is uniquely positioned to supply. Our materials ensure the requisite purity, low strain, and mechanical integrity needed for realizing long-coherence quantum processors.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate and extend the high-fidelity entanglement generation demonstrated in this research, 6CCVD recommends:
- Optical Grade Single Crystal Diamond (SCD): Essential for maximizing NV center ensemble coherence (T2) and relaxation times (T1) up to the reported 1-second regimes. Our SCD features extremely low nitrogen and defect concentrations, crucial for minimal dephasing.
- Low-Loss Electronic Grade Substrates: High-purity, low-strain SCD is the ideal substrate material for fabricating high-Q superconducting resonators and flux qubits, minimizing dielectric loss and decoherence that plague traditional semiconductor platforms.
- Custom Wafer Thickness: To accommodate complex 3D cQED architectures or robust handling, 6CCVD can supply SCD substrates up to 500 ”m thick, and specialized substrates up to 10 mm.
Customization Potential
Section titled âCustomization PotentialâThe integration of flux qubits and resonators on solid-state memories requires tight control over material dimensions, surface preparation, and circuit interface engineering.
| Requirement/Feature | 6CCVD Capability | Research Relevance |
|---|---|---|
| Substrate Dimensions | Plates/wafers up to 125 mm (PCD). SCD wafers optimized for NV fabrication. | Required for scalable, inch-size cQED fabrication. |
| Surface Finish | Polishing to Ra < 1 nm (SCD). | Essential for minimizing surface losses at the superconductor-diamond interface. |
| Interface Metalization | Custom metal deposition (Au, Pt, Pd, Ti, W, Cu). | Necessary for defining flux qubit loops, CPW resonators, and ensuring low-resistance contacts between the qubit and memory components. |
| Custom Thickness Control | SCD thickness from 0.1 ”m up to 500 ”m, enabling precise control over cavity coupling strength and thermal management. | Required for tuning coupling capacitances (C1, C2) and integrating thin-film circuits. |
Engineering Support
Section titled âEngineering SupportâThis research successfully demonstrates the potential of utilizing diamond-based NV ensembles for complex quantum information processing tasks, such as high-fidelity generation of entangled coherent states (98.5%).
6CCVDâs in-house team of PhD material scientists specializes in optimizing MPCVD growth parameters for NV generation, low-strain material, and cQED integration. We can assist engineers and scientists with:
- Material Selection: Guiding the choice between SCD or highly polished PCD based on specific coherence and cost requirements for hybrid cQED projects.
- Surface Preparation: Providing specialized preparation services to ensure optimal growth and alignment of superconducting films (Ti/Nb/Al) on diamond surfaces.
- Custom NV Doping: Controlling nitrogen incorporation during growth to optimize NV ensemble density and uniformity for enhanced memory coupling strengths (”k).
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In a recent remarkable experiment [Sci. Adv. 2, e1501531 (2016)], a 3-qubit quantum Fredkin (i.e., controlled-SWAP) gate was demonstrated by using linear optics. Here we propose a simple experimental scheme by utilizing the dispersive interaction in superconducting quantum circuit to implement a hybrid Fredkin gate with a superconducting flux qubit as the control qubit and two separated quantum memories as the target qudits. The quantum memories considered here are prepared by the superconducting coplanar waveguide resonators or nitrogen-vacancy center ensembles. In particular, it is shown that this Fredkin gate can be realized using a single-step operation and more importantly, each target qudit can be in an arbitrary state with arbitrary degrees of freedom. Furthermore, we show that this experimental scheme has many potential applications in quantum computation and quantum information processing such as generating arbitrary entangled states (discrete-variable states or continuous-variable states) of the two memories, measuring the fidelity and the entanglement between the two memories. With state-of-the-art circuit QED technology, the numerical simulation is performed to demonstrate that two-memory NOON states, entangled coherent states, and entangled cat states can be efficiently synthesized.