By Aalyia Shaukat, contributing writer
Researchers at the University of New South Wales (USNW) in Sydney, Australia, recently developed a chip design for a quantum computer that leverages conventional silicon CMOS transistor designs, combining the budding world of quantum computing with the matured silicon technology industry.
While large-scale quantum computing may be decades away, this new design can be a significant step in the right direction because silicon-based chip fabrication is highly scalable with predictable performance. The design, described in a Nature article, uses transistor-based circuits to control charge-storage electrodes that can adjust a qubits spin. The qubits in this system are defined by the spin state of electrons confined in quantum dots — or extremely small semiconductor particles that are nanometers in size. The chip is designed such that the transistor circuitry is used to control the quantum circuit on the bottom layer.
The innate edge that quantum computing has over traditional computers stems from the concepts of superposition and entanglement. While a traditional computer’s hardware is limited to transistor logic of 0’s or 1’s, quantum computation uses quantum bits (qubits) that are both a 0 and a 1 simultaneously. Because qubits contain multiple states at the same time, quantum computers can perform millions of computations while the conventional PC performs only one. Entanglement allows for a heightened correlation between particles because quantum particles do not act independently of each other. In other words, if two particles exist in a system and one is observed, the remaining particle is instantly assessed because they are “entangled,” immediately cutting down the processing necessary by 50%. This correlation only increases with the number of qubits where, in a system with n qubits, there are 2n correlations. Even with the massive potential processing power of quantum computers, the commercialization of this technology requires significant technological leaps.
“Our design incorporates conventional silicon transistor switches to ‘turn on’ operations between qubits in a vast two-dimensional array, using a grid-based ‘word’ and ‘bit’ select protocol similar to that used to select bits in a conventional computer memory chip,” said Professor Andrew Dzurak, a Program Leader at Australia’s Centre of Excellence for Quantum Computation and Communication Technology (CQC2T). “By selecting electrodes above a qubit, we can control a qubit’s spin, which stores the quantum binary code of a 0 or 1. And by selecting electrodes between the qubits, two-qubit logic interactions, or calculations, can be performed between qubits.” This has the potential to overcome one of the main hurdles toward the proliferation of quantum computer technology — scaling up the size and processing power while maintaining thousands of qubits coherently coupled.
Quantum coherence leads to the quality of quantum entanglement, which is essential for solving extremely complex problems. Quantum error correction (QEC), a technique that allows for quantum simulations using the noisy qubits’ found reality, actually assists in surmounting this obstacle given that the error is below a certain threshold. Still, a platform that remains functional while being scaled up to larger dimensions is required in order for quantum computers to be able to utilize the advantages of QEC.
“Our chip blueprint incorporates a new type of error-correcting code designed specifically for spin qubits and involves a sophisticated protocol of operations across the millions of qubits,” said Dzurak. “It’s the first attempt to integrate into a single chip all of the conventional silicon circuitry needed to control and read the millions of qubits needed for quantum computing.” The UNSW chip design integrates the qubit and control electronics monolithically, generating a potentially scalable qubit array. Still, this has yet to be fabricated and tested for performance, and they’ve already received a whole lot of backing for just that.
This year the founders of this project, Menno Veldhorst and Andrew Dzurak, launched Australia’s first quantum computing company, Silicon Quantum Computing Pty Ltd, with the goal to develop a 10-qubit silicon quantum integrated circuit (IC) by 2022. They’ve already managed to gather A$83 million in backing: The USNW has pledged A$25 million, New South Wales (NSW) government granted A$8.7 million, Commonwealth Bank A$14 million, Telstra A$10 million, and the Australian government donated another A$25 million.
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