[Paper Review] Superconducting qutrit-qubit circuit: A toolbox for efficient quantum gates

Thomas Bækkegaard, Lasse Bjørn Kristensen+4 more|arXiv (Cornell University)|Feb 12, 2018

Quantum Computing Algorithms and Architecture3 citations

TL;DR

This paper proposes a superconducting qutrit-qubit circuit that enables efficient, robust, and universal quantum gates by coupling a three-level system (qutrit) to two qubits, allowing implementation of entanglement, Toffoli and Fredkin gates, and conditional geometric (holonomic) gates—offering a scalable toolbox for large-scale quantum computation with reduced decoherence risk.

ABSTRACT

As classical computers struggle to keep up with Moore's law, quantum computing may represent a big step in technology and yield significant improvement over classical computing for many important tasks. Building a quantum computer, however, is a daunting challenge since it requires good control but also good isolation from the environment to minimize decoherence. It is therefore important to realize quantum gates efficiently, using as few operations as possible, to reduce the amount of required control and operation time and thus improve the quantum state coherence. Here we propose a superconducting circuit for implementing a tunable spin chain consisting of a qutrit (three-level system analogous to spin-1) coupled to two qubits (spin-1/2). Our system can efficiently accomplish various quantum information tasks, including generation of entanglement of the two qubits and conditional three-qubit quantum gates, such as the Toffoli and Fredkin gates, which are universal for reversible classical computations. Furthermore, our system realizes a conditional geometric gate which may be used for holonomic (non-adiabatic) quantum computing. The efficiency, robustness and universality of our circuit makes it a promising candidate to serve as a building block for larger spin networks capable of performing involved quantum computational tasks.

Motivation & Objective

• To address the challenge of decoherence in quantum computing by minimizing gate operation time and control complexity.
• To develop a tunable spin chain architecture using a qutrit coupled to two qubits for enhanced gate efficiency.
• To realize universal quantum gates, including Toffoli and Fredkin gates, for reversible classical computation.
• To implement a conditional geometric gate for non-adiabatic holonomic quantum computing.
• To create a scalable building block for larger spin networks capable of complex quantum tasks.

Proposed method

• Designing a superconducting circuit with a tunable qutrit (three-level system) coupled to two qubits (spin-1/2) to form a tunable spin chain.
• Utilizing dynamic coupling control to engineer interactions between the qutrit and qubits for gate operations.
• Implementing conditional quantum gates via controlled interactions mediated by the qutrit's intermediate level.
• Leveraging geometric (Berry) phase accumulation for holonomic gate operations to enhance robustness against certain errors.
• Engineering the system's level structure and coupling strengths to enable universal gate sets including Toffoli and Fredkin gates.
• Ensuring gate fidelity and coherence by minimizing operation time and reducing environmental coupling through efficient gate design.

Experimental results

Research questions

• RQ1 Can a superconducting qutrit-qubit system efficiently implement universal quantum gates with reduced operation time and control complexity?
• RQ2 How can conditional geometric gates be realized in a superconducting circuit to enable non-adiabatic holonomic quantum computing?
• RQ3 To what extent can the qutrit-qubit architecture generate entanglement and implement Toffoli and Fredkin gates?
• RQ4 What is the role of the qutrit’s intermediate level in mediating multi-qubit interactions and enabling gate universality?
• RQ5 Can this architecture serve as a scalable building block for larger quantum spin networks?

Key findings

• The proposed qutrit-qubit circuit enables efficient implementation of two-qubit entanglement with reduced gate time and control overhead.
• The system realizes universal quantum gates, including the Toffoli and Fredkin gates, which are essential for reversible classical computation.
• A conditional geometric gate is achieved, supporting non-adiabatic holonomic quantum computing with potential error resilience.
• The architecture demonstrates robustness due to reduced operation time, which enhances quantum state coherence.
• The circuit structure provides a scalable platform for constructing larger spin networks capable of performing complex quantum computational tasks.
• The tunable coupling between the qutrit and qubits allows dynamic control of interactions, enabling versatile gate operations.