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IEEE Nanotechnology Magazine

A Computational Analysis on 5-Qubit Quantum Circuits Designed With Electron Spins in Silicon

Junghee Ryu, Hoon Ryu

Published Oct 30, 2024• 1 citation
Publisher

Abstract

We computationally investigate the programmability of quantum circuits that are manipulated with electron spins in semiconductor devices based on the silicon/silicon-germanium heterostructure. Using our multi-scale modeling approach whose workloads are fairly accelerated with a parallel computing, we design an electrically defined quantum dot structure that confines up to 5 electron spins with bias controls, and calculate the sets of electrical biases that serve as the standard operation modes that can initialize the system with weakly or strongly correlated spins. With the secured operation modes, we discuss how essential universal gates can be implemented, and demonstrate end-to-end operations of two different 5-qubit algorithm circuits. This work not only reveals the fundamental guidelines for designs of silicon quantum processors that may not be easy to be procured directly from existing commercial softwares or experiments, but presents the details of a practical method for a computational analysis of quantum information processing in silicon devices that would be hard to be conducted withab-initiosimulations.

DOI
10.1109/mnano.2024.3475889

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We computationally investigate the programmability of quantum circuits that are manipulated with electron spins in semiconductor devices based on the silicon/silicon-germanium heterostructure. Using our multi-scale modeling approach whose workloads are fairly accelerated with a parallel computing, we design an electrically defined quantum dot structure that confines up to 5 electron spins with bias controls, and calculate the sets of electrical biases that serve as the standard operation modes that can initialize the system with weakly or strongly correlated spins. With the secured operation modes, we discuss how essential universal gates can be implemented, and demonstrate end-to-end operations of two different 5-qubit algorithm circuits. This work not only reveals the fundamental guidelines for designs of silicon quantum processors that may not be easy to be procured directly from existing commercial softwares or experiments, but presents the details of a practical method for a computational analysis of quantum information processing in silicon devices that would be hard to be conducted withab-initiosimulations.
With recent experimental advancements demonstrating high-fidelity universal logic gates and basic programmability, silicon-based spin quantum bits (qubits) have emerged as promising candidates for scalable quantum computing. However, implementation of more complex quantum information protocols with many qubits still remains a critical challenge for realization of practical programmability in silicon devices. In this study, we present a computational investigation of entanglement-based quantum information applications implemented on an electrically defined quantum dot structure in silicon. Using in-house multi-scale simulations based on tight-binding calculations augmented with classical physics with bulk properties, we model a five quantum dot system that can create up to five electron spin qubits, and discuss details of control engineering needed to implement single-qubit rotations and two-qubit logic operations in a programmable manner. Using these elementary operations, we design a five-qubit quantum teleportation protocol and computationally verify its end-to-end operation including a simple but clear analysis on how the designed circuit can be affected by charge noise. With engineering details that are not well uncovered by experiments, our results demonstrate the advanced programmability of silicon quantum dot systems, delivering the practical guidelines for potential designs of quantum information processes based on electrically defined silicon quantum dot structures.
The simplicity of encoding a qubit in the state of a single electron spin and the potential for their integration into industry-standard microchips continue to drive the field of semiconductor-based quantum computing. After a series of key first-principles demonstrations validating universal gate operations, initialization and readout, three-qubit algorithms have already been realized with silicon-based quantum dots in past years. Devices containing more qubits have become available since then but experiments have not gone beyond meeting the DiVincenzo criteria. In this work, we fully exploit the capacity of a spin-qubit array and implement a six-qubit quantum circuit, the largest utilizing semiconductor quantum technology. By programming the quantum processor, we execute quantum circuits across all permutations of three, four, five, and six neighboring qubits, demonstrating successful programmable multi-qubit operation throughout the array. Using an error model that incorporates quasi-static noise allows us to qualitatively explain some key trends in our experimental results and highlight the necessity to minimize idling times through simultaneous operations, extending dephasing times, and consistently improving state preparation and measurement fidelities.
Though electron spins in electrically defined silicon (Si) quantum dot systems have been extensively employed for physical realization of quantum processing units, their application to quantum sensing has not been active compared to the case of photonic qubits and nitrogen-vacancy spins in diamonds. This work presents a comprehensive study on the feasibility of Si quantum dot structures as a physical platform for implementation of a sensing protocol for magnetic fields. To examine sensing operations at a systematic level, we adopt in-house device simulations taking a Si double quantum dot (DQD) system as a target device where the confinement of electron spins is controlled with electrical biases in a Si/Si-germanium heterostructure. Simulation results demonstrate the fairly nice utility of the Si DQD platform for detecting externally presented static magnetic fields, and, more notably, reveal that sensing operations are not quite vulnerable to charge noise that is omnipresent in solid materials. As a rare study that presents in-depth discussion on operations of quantum sensing units at a device-level based on computational modeling, this work can deliver practical insights for potential designs of sensing units with electron spins in Si devices.
Recent advances in quantum error correction codes for fault-tolerant quantum computing and physical realizations of high-fidelity qubits in multiple platforms give promise for the construction of a quantum computer based on millions of interacting qubits. However, the classical-quantum interface remains a nascent field of exploration. Here, we propose an architecture for a silicon-based quantum computer processor based on complementary metal-oxide-semiconductor (CMOS) technology. We show how a transistor-based control circuit together with charge-storage electrodes can be used to operate a dense and scalable two-dimensional qubit system. The qubits are defined by the spin state of a single electron confined in quantum dots, coupled via exchange interactions, controlled using a microwave cavity, and measured via gate-based dispersive readout. We implement a spin qubit surface code, showing the prospects for universal quantum computation. We discuss the challenges and focus areas that need to be addressed, providing a path for large-scale quantum computing.
Abstract Recent advances in quantum error correction codes for fault-tolerant quantum computing and physical realizations of high-fidelity qubits in multiple platforms give promise for the construction of a quantum computer based on millions of interacting qubits. However, the classical-quantum interface remains a nascent field of exploration. Here, we propose an architecture for a silicon-based quantum computer processor based on complementary metal-oxide-semiconductor (CMOS) technology. We show how a transistor-based control circuit together with charge-storage electrodes can be used to operate a dense and scalable two-dimensional qubit system. The qubits are defined by the spin state of a single electron confined in quantum dots, coupled via exchange interactions, controlled using a microwave cavity, and measured via gate-based dispersive readout. We implement a spin qubit surface code, showing the prospects for universal quantum computation. We discuss the challenges and focus areas that need to be addressed, providing a path for large-scale quantum computing.
Quantum dots can confine single electrons or holes to define spin qubits that can be operated with high fidelity. Experimental work has progressed from linear to two-dimensional arrays of quantum dots, enabling qubit interactions that are essential for quantum simulation and computation. Here, we explore architectures beyond planar geometries by constructing quantum dot arrays in three dimensions. We realize an eight-quantum dot system in a silicon-germanium heterostructure comprising two stacked germanium quantum wells, where quantum dots are positioned at the vertices of a cuboid. Using electrostatic gate control, we load a single hole into any of the eight quantum dots. To demonstrate the potential of multilayer quantum dot systems, we show coherent spin control and hopping-induced spin rotations by shuttling between the quantum wells. The ability to extend quantum dot arrays in three dimensions provides opportunities for novel quantum hardware and high-connectivity quantum circuits.