Hitachi Cambridge Labs Tackles the Challenge of Building a Large-Scale Quantum Computer

By Hubert Yoshida posted 04-07-2021 19:35

  
Quantum computers promise to have a major positive impact on society. How else will we have the capability to process the exabytes of data and turn it into useful information to develop new cures for cancer, improve security, and boost artificial intelligence. However, building the hardware that will enable that paradigm change is one of the greatest technological challenges facing humanity.

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In 2019, which seems like a lifetime ago due to the Pandemic, Google announced that their quantum computer was the first to perform a calculation that would be practically impossible for a classical supercomputer. This is known as Quantum Supremacy. Its quantum computer, known as “Sycamore”, carried out a specific calculation that is beyond the practical capabilities of regular, ‘classical’ machines. They estimate that the same calculation would take even the best classical supercomputer 10,000 years to complete. However, the problem that was solved was not a practical application and was more proof of concept.

Quantum computers work in a fundamentally different way from classical computers where a classical bit is either a 1 or a 0.  In a Quantum computer, a quantum bit, or qubit, can exist in multiple states at once. This capability allows for the construction of an exponentially large computing space with only a linear number of resources, Qubits, making it exponentially more powerful than conventional computing for a specific set of tasks. When qubits are inextricably linked, physicists can, in theory, exploit the interference between their wave-like quantum states to perform calculations that might otherwise take millions of years.  

The one of the drawbacks with current Quantum computers is noise because it can make qubits change state at times and in ways that programmers did not intend, leading to computational errors. Most interactions with the surrounding environment, such as charge instabilities and thermal fluctuations, are sources of qubit noise. All of them can compromise information. The algorithms used by quantum computers must spend resources, qubits, to correct for this noise. Current systems are still relatively simple and as such their performance is far from what supercomputers can achieve. The first wave of development, known as noisy intermediate-scale quantum (NISQ) technology, is being led by two key technologies: ion traps and superconductors. Ion traps use single charged atoms trapped in electromagnetic fields as qubits. Superconductors are electrical resonators that can oscillate in two different manners simultaneously. Ion traps are being explored by companies like IonQ, Inc., Alpine Quantum Technologies, GmbH., and Honeywell International Inc., whereas superconductors are being worked on by International Business Machines Corporation (IBM), Google LLC, Alibaba Group Holding Limited, Intel Corporation, and Rigetti & Co, Inc. Systems using NISQ technology have been successfully demonstrated with up to a few tens of qubits working simultaneously. The power of a quantum computer is rated by the number of qubits that it manages. Google’s Sycamore had 64 qubits.

While Google was able to achieve Quantum Supremacy with Sycamore, the problem that was solved has little practical application. In order to run the quantum algorithms that can make a real impact in society would require orders of magnitude of qubits. Predictions estimate that 102 to 103 qubits are needed to run a simulation of a simple material, and 106 to 108 qubits for an arbitrarily complex one. Scaling up to such a large number of qubits is the greatest challenge to overcome in order to fulfill the promise of quantum computing. Ion trap and superconducting qubits offer limited prospects for scalability beyond the NISQ era with current qubit densities of just 1 and 100 qubits/cm2 respectively. This translates into machines the size of a whole room or even a football stadium.

The Hitachi Cambridge Laboratory (HCL) is developing a new technology that has the potential to solve the scaling problem, making it a leading hardware candidate for building the first general-purpose quantum computer. (Hitachi established the Hitachi Cambridge Laboratory (HCL) in collaboration with the Cavendish Laboratory of the University of Cambridge in 1985)
HCL is using silicon transistors, the omnipresent device in all microprocessors, to make scalable qubits. One of the advantages of silicon is that it offers a relatively noise-free environment where spins can retain their quantum nature. This means that less resources will be required for error correction.

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The biggest attraction of silicon-based quantum processors is the ability to leverage the same technology that the microchip industry has handled for the past 60 years. This means manufacturers can expect to benefit from previous multibillion-dollar infrastructure investments, keeping production costs low. By using silicon as a basis for a quantum computer means that all the clever engineering and processing that went into developing modern classical microelectronics – from dense device packaging to integrated interconnect routing – can be adapted and used to build quantum devices. By using the same technology that is used in conventional computing, HCL aims to deliver a cost-effective chip-size solution with an unparalleled qubit density of 108 qubits/cm2, one that could be manufactured in large quantities in silicon foundries. The proposed solution will open up quantum computing to many new companies by transferring the successful fabless business model from the microelectronics industry to the field of quantum nano electronics.

At the Hitachi Cambridge Laboratory, the Quantum Information Team is tackling this challenge using complementary metal-oxide semiconductor technology, the same transistor technology used in all conventional information processing devices, such as mobile phones, computers, and cars. By using the spin of single electrons trapped in these transistors at very low temperatures, the Quantum Information Team aims to deliver a scalable solution while also reducing the cost of development.

For more information on this approach read the following article from Phys.org:
Quantum computers could arrive sooner if we build them with traditional silicon technology
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05-04-2022 11:53

Great one

04-27-2022 02:50

Very informative