https://news.ku.dk/all_news/2021/10/innovative-chip-built-by-ucph-physicists-resolves-quantum-headache/ * Topic navigation * Content * Footer links Start Toggle navigation * Map * Phone Book * KUnet * Dansk * Study at UCPH + Bachelor's programmes + Master's programmes + Visiting students + PhD programmes + Online courses + Course search * Research + Researchers and publications + PhD programmes + Research centres * News + Companies recruit more female board members through family ties Companies recruit more female board members through family ties 2021.10.21 + Origin of domestic horses finally established Origin of domestic horses finally established 2021.10.20 + Economics of climate change: One per cent makes a world of difference Economics of climate change: One per cent makes a world of difference 2021.10.13 + All news + Press service * Collaboration + Research collaboration + International alliances + Innovation and entrepreneurship + Alumni * Employment + Job portal + Career for young researchers + For international employees * About UCPH + Profile and history + Facts and figures + Organisation + Faculties + Departments + Contact Kobenhavns Universitet News [ ] News * Society, Politics & Law * Nature, Numbers & Technology * Culture, Language & History * Health, Body & Mind * University Life * Contact * Press service * News * All news * Innovative chip built ... 28 October 2021 Innovative chip built by UCPH physicists resolves quantum headache quantum technology Quantum physicists at the University of Copenhagen are reporting an international achievement for Denmark in the field of quantum technology. By simultaneously operating multiple spin qubits on the same quantum chip, they surmounted a key obstacle on the road to the supercomputer of the future. The result bodes well for the use of semiconductor materials as a platform for solid-state quantum computers. The research team Federico Fedele, Anasua Chatterjee and Ferdinand Kuemmeth. One of the engineering headaches in the global marathon towards a large functional quantum computer is the control of many basic memory devices - qubits - simultaneously. This is because the control of one qubit is typically negatively affected by simultaneous control pulses applied to another qubit. Now, a pair of young quantum physicists at the University of Copenhagen's Niels Bohr Institute -PhD student, now Postdoc, Federico Fedele, 29 and Asst. Prof. Anasua Chatterjee, 32,- working in the group of Assoc. Prof. Ferdinand Kuemmeth, have managed to overcome this obstacle. Global qubit research is based on various technologies. While Google and IBM have come far with quantum processors based on superconductor technology, the UCPH research group is betting on semiconductor qubits - known as spin qubits. "Broadly speaking, they consist of electron spins trapped in semiconducting nanostructures called quantum dots, such that individual spin states can be controlled and entangled with each other", explains Federico Fedele. About qubits The brain of the quantum computer that scientists are attempting to build will consist of many arrays of qubits, similar to the bits on smartphone microchips. They will make up the machine's memory. The famous difference is that while an ordinary bit can either store data in the state of a 1 or 0, a qubit can reside in both states simultaneously - known as quantum superposition - which makes quantum computing exponentially more powerful. Spin qubits have the advantage of maintaining their quantum states for a long time. This potentially allows them to perform faster and more flawless computations than other platform types. And, they are so miniscule that far more of them can be squeezed onto a chip than with other qubit approaches. The more qubits, the greater a computer's processing power. The UCPH team has extended the state of the art by fabricating and operating four qubits in a 2x2 array on a single chip. Circuitry is 'the name of the game' Thus far, the greatest focus of quantum technology has been on producing better and better qubits. Now it's about getting them to communicate with each other, explains Anasua Chatterjee: "Now that we have some pretty good qubits, the name of the game is connecting them in circuits which can operate numerous qubits, while also being complex enough to be able to correct quantum calculation errors. Thus far, research in spin qubits has gotten to the point where circuits contain arrays of 2x2 or 3x3 qubits. The problem is that their qubits are only dealt with one at a time." It is here that the young quantum physicists' quantum circuit, made from the semiconducting substance gallium arsenide and no larger than the size of a bacterium, makes all the difference: "The new and truly significant thing about our chip is that we can simultaneously operate and measure all qubits. This has never been demonstrated before with spin qubits - nor with many other types of qubits," says Chatterjee, who is one of two lead authors of the study, which has recently been published in the journal Physical Review X Quantum. Size comparison of qubits The illustration shows the size difference between spin qubits and superconducting qubits. Being able to operate and measure simultaneously is essential for performing quantum calculations. Indeed, if you have to measure qubits at the end of a calculation - that is, stop the system to get a result - the fragile quantum states collapse. Thus, it is crucial that measurement is synchronous, so that the quantum states of all qubits are shut down simultaneously. If qubits are measured one by one, the slightest ambient noise can alter the quantum information in a system. About the chip The four spin qubits in the chip are made of the semiconducting material gallium arsenide. Situated between the four qubits is a larger quantum dot that connects the four qubits to each other, and which the researchers can use to tune all of the qubits simultaneously. Milestone The realization of the new circuit is a milestone on the long road to a semiconducting quantum computer. "To get more powerful quantum processors, we have to not only increase the number of qubits, but also the number of simultaneous operations, which is exactly what we did" states Professor Kuemmeth, who directed the research. At the moment, one of the main challenges is that the chip's 48 control electrodes need to be tuned manually, and kept tuned continuously despite environmental drift, which is a tedious task for a human. That's why his research team is now looking into how optimization algorithms and machine learning could be used to automate tuning. To allow fabrication of even larger qubit arrays, the researchers have begun working with industrial partners to fabricate the next generation of quantum chips. Overall, the synergistic efforts from computer science, microelectronics engineering, and quantum physics may then lead spin qubits to the next milestones. Contact Anasua Chatterjee Assistant Professor Center for Quantum Devices - Niels Bohr Institute University of Copenhagen anasua.chatterjee@nbi.ku.dk +45 35 33 53 70 Ferdinand Kuemmeth Associate Professor Center for Quantum Devices - Niels Bohr Institute University of Copenhagen kuemmeth@nbi.ku.dk +45 21 16 26 57 Maria Hornbek Journalist Faculty of Science University of Copenhagen maho@science.ku.dk +45 22 95 42 83 More stories [3841208] Quantum physics Major breakthrough: Copenhagen researchers can now achieve 'quantum advantage' [3960533] QUANTUM RESEARCH New invention keeps qubits of light stable at room temperature --------------------------------------------------------------------- Communication University of Copenhagen Norregade 10, PO Box 2177 1017 Copenhagen K Contact: Media team medieteam@adm.ku.dk * University of Copenhagen * Management * Administration * Faculties * Departments * Research centres * Animal hospitals * School of Dentistry * Libraries * Museums Contact * Map * Find an employee * Contact UCPH Services * Press and media service * Merchandise * UCPH apps * IT-support * For suppliers For students and employees * KUnet Job and career * Job portal * Alumni Emergencies * Emergency response Web * Cookies and privacy policy * Accessibility statement * Information security Connect with UCPH