{"id":35620,"date":"2023-01-16T11:55:53","date_gmt":"2023-01-16T12:55:53","guid":{"rendered":"https:\/\/peymantaeidi.net\/stem-cell\/?p=35620"},"modified":"2023-01-16T13:37:01","modified_gmt":"2023-01-16T13:37:01","slug":"billion-qubit-quantum-chips-now-closer-with-new-spin-control-method","status":"publish","type":"post","link":"https:\/\/peymantaeidi.net\/stem-cell\/2023\/01\/16\/billion-qubit-quantum-chips-now-closer-with-new-spin-control-method\/","title":{"rendered":"Billion-qubit quantum chips now closer with new spin control method"},"content":{"rendered":"
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UNSW Sydney<\/a> engineers have discovered a new way of precisely controlling single electrons in quantum dots that run logic gates. The new mechanism is also less bulky and requires fewer parts, which could prove essential to making large-scale silicon quantum computers<\/a> a reality.<\/strong><\/p>\n

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\"Illustration<\/p>\n

Illustration showing how multiple qubits might be controlled using the new quantum intrinsic spin-orbit EDSR process. Image credit: Tony Melov\/UNSW<\/p>\n<\/div>\n

The serendipitous discovery, made by engineers at the quantum computing start-up Diraq<\/a> and UNSW, is detailed in the journal Nature <\/em>Nanotechnology<\/em><\/a>.<\/p>\n

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\u201cThis was a completely new effect we\u2019d never seen before, which we didn\u2019t quite understand at first,\u201d said lead author Dr Will Gilbert, a quantum processor engineer at Diraq, a UNSW spin-off company based at its Kensington campus. \u201cBut it quickly became clear that this was a powerful new way of controlling spins in a quantum dot. And that was super exciting.\u201d<\/p>\n

Logic gates are the basic building block of all computation. They allow \u2018bits\u2019 \u2013 or binary digits (0s and 1s) \u2013 to work together to process information. However, a quantum<\/em> bit (or qubit) exists in both of these states at once \u2013 a condition known as a \u2018superposition\u2019.<\/p>\n

This allows a multitude of computation strategies \u2013 some exponentially faster, some operating simultaneously \u2013 that are beyond classical computers. Qubits are made up of \u2018quantum dots\u2019 \u2013 tiny nanodevices that can trap one or a few electrons. Precise control of the electrons is necessary for computation to occur.<\/p>\n

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Using electric rather than magnetic fields<\/strong><\/h2>\n

While experimenting with different geometrical combinations of devices just billionths of a metre in size that control quantum dots, along with various types of miniscule magnets and antennas that drive their operations, Dr Tuomo Tanttu<\/a> from UNSW Engineering<\/a> stumbled across a strange effect.<\/p>\n

\u201cI was trying to really accurately operate a two-qubit gate, iterating through a lot of different devices, slightly different geometries, different materials stacks and different control techniques,\u201d said Dr Tanttu, who is also a measurement engineer at Diraq. \u201cThen this strange peak popped up. It looked like the rate of rotation for one of the qubits was speeding up, which I\u2019d never seen in four years of running these experiments.\u201d<\/p>\n

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What he had discovered, the engineers later realised, was a new way of manipulating the quantum state of a single qubit by using electric fields, rather than the magnetic fields they had been using previously. Since the discovery was made in 2020, the engineers have been perfecting the technique \u2013 which has become another tool in their arsenal to fulfil Diraq\u2019s ambition of building billions of qubits on a single chip.<\/p>\n

\u201cThis is a new way to manipulate qubits, and it\u2019s less bulky to build \u2013 you don\u2019t need to fabricate cobalt micro-magnets or an antenna right next to the qubits to generate the control effect,\u201d said Dr Gilbert. \u201cIt removes the requirement of placing extra structures around each gate. So, there\u2019s less clutter.\u201d<\/p>\n

Controlling single electrons without disturbing others nearby is essential for quantum information processing in silicon. There are two established methods: electron spin resonance (ESR) using an on-chip microwave antenna, and electric dipole spin resonance (EDSR), which relies on an induced gradient magnetic field. The newly discovered technique is known as \u2018intrinsic spin-orbit EDSR\u2019.<\/p>\n

\u201cNormally, we design our microwave antennas to deliver purely magnetic fields,\u201d said Dr Tanttu. \u201cBut this particular antenna design generated more of an electric field than we wanted \u2013 but that turned out to be lucky, because we discovered a new effect we can use to manipulate qubits. That\u2019s serendipity for you.\u201d<\/p>\n

Building on making quantum computing in silicon a reality<\/strong><\/h2>\n

\u201cThis is a gem of a new mechanism, which just adds to the trove of proprietary technology we\u2019ve developed over the past 20 years of research,\u201d said Professor Andrew Dzurak<\/a>, Scientia Professor in Quantum Engineering at UNSW and CEO and founder of Diraq. Professor Dzurak led the team that built the first quantum logic gate in silicon<\/a> in 2015.<\/p>\n

\u201cIt builds on our work to make quantum computing in silicon a reality, based on essentially the same semiconductor component technology as existing computer chips, rather than relying on exotic materials.<\/p>\n

\u201cSince it\u2019s based on the same CMOS technology as today\u2019s computer industry, our approach will make it easier and faster to scale up for commercial production and achieve our goal of fabricating billions of qubits on a single chip.\u201d<\/p>\n

CMOS (or complementary metal-oxide-semiconductor, pronounced \u201csee-moss\u201d) is the fabrication process at the heart of modern computers. It\u2019s used for making all sorts of integrated circuit components \u2013 including microprocessors, microcontrollers, memory chips and other digital logic circuits, as well as analogue circuits such as image sensors and data converters.<\/p>\n

Building a quantum computer has been called the \u2018space race of the 21st century\u2019 \u2013 a difficult and ambitious challenge with the potential to deliver revolutionary tools for tackling otherwise impossible calculations, such as the design of complex drugs and advanced materials, or the rapid search of massive, unsorted databases.<\/p>\n

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\u201cWe often think of landing on the Moon as humanity\u2019s greatest technological marvel,\u201d said Professor Dzurak. \u201cBut the truth is, today\u2019s CMOS chips \u2013 with billions of operating devices integrated together to work like a symphony, and that you carry in your pocket \u2013 is an astounding technical achievement and revolutionised modern life. Quantum computing will be equally astonishing.\u201d<\/p>\n

Source: UNSW<\/a><\/p>\n<\/p><\/div>\n