How can the transistors in your smartphone form quantum dots?
Quantum engineering likely holds the key to the next technological revolution. But this does not necessarily require developing new technologies from scratch. At the University of Toronto in Canada, Professor Sorin Voinigescu and his team are investigating whether the transistors in everyday electronic devices can advance the field of quantum computing. By supercooling these commercial transistors, they are creating quantum dots.
Talk like a quantum engineer
Cryogenic — related to very low temperatures (below -150 °C)
Discrete energy level — a specific, fixed energy state (also known as an electron shell) that an electron can occupy within an atom
Hole — the absence of an electron in an atom
Nanometre (nm) — one billionth of a metre, or 0.000001 mm
Quantum dot — a semiconductor nanostructure populated by a single particle, electron or hole which, in the presence of a magnetic field, becomes a qubit
Quantum physics — the study of matter and energy at the atomic and subatomic level
Qubit — the basic unit of information in quantum computing
Semiconductor — a material that can have the properties of a conductor or insulator, depending on its composition and conditions
Spin — a quantum property of subatomic particles
Superposition — the ability of a quantum system to be in multiple states at the same time
Transistor — a nanoscale semiconductor device used as a switch to control electrical currents in circuits
Transistors are a critical component of all computers. Made from semiconducting materials, transistors are electronic switches which allow the computer to encode binary digits, or ‘bits’. Modern smartphones contain over 10 billion transistors in their circuitry. These transistors are incredibly small – only a few nanometres wide. And, when things get very small, the laws of physics appear different to those we encounter at larger scales. This is where we enter the realm of quantum physics. At the University of Toronto, Professor Sorin Voinigescu and his team are exploring how transistors can take on quantum properties. By acting as quantum dots, Sorin believes commercial transistors could advance the field of quantum computing.
What are quantum dots?
A quantum dot is a nanoscale structure formed, under specific conditions, in the smallest transistors. “Within a quantum dot, electrons (which carry a negative charge) or holes (which carry a positive charge) can only occupy discrete energy levels,” explains Sorin. In classical computers, the charge of electrons and holes is used to encode information in bits. However, electrons and holes also have the quantum property of spin. In quantum computers, the spin of electrons and holes is used to encode information in quantum bits, or ‘qubits’.
“Qubits are in a superposition of two states: spin-up and spin-down,” explains Sorin. “However, in a quantum dot, the two spin states of the electron or hole are indistinguishable because they occupy the same energy level.” If a magnetic field is applied to the quantum dot, each discrete energy level becomes either spin-up or spin-down, and the electrons and holes at each level have the corresponding spin state. The lowest two energy levels form the basis states of a qubit.
How do transistors produce qubits?
“We take the smallest transistors found in smartphones and laptops and supercool them to below 77 K (-196 °C),” explains Sorin. “At these very low temperatures, they behave as quantum dots. Then, by applying a magnetic field perpendicular to the transistor, the quantum dots produce qubits in which quantum computer operations can be performed.” This means that, depending on the surrounding environment, the transistors in your smartphone can behave as classical transistors, quantum dots or qubits.
How does the team study quantum dots?
Sorin and his team use computer-aided modelling to design qubit arrays on transistors. “For example, we might try different sizes of quantum dots to understand how different dimensions affect their properties,” says Shai Bonen, one of the first graduate students to begin the quantum dot research in Sorin’s lab. These designs are submitted to a commercial semiconductor foundry, which manufactures the transistors according to the team’s specifications.
When the completed transistors are returned from the foundry, the team uses liquid helium to supercool them to about 2 K (-271 °C). “We measure the supercooled transistors with cryogenic probes to test the quality of the qubits they produce,” explains Janelle Frias, an undergraduate student in the lab. “We are interested in the qubits’ lifetime (how long they stay in a given state) and frequencies (which describe how the qubit state evolves).” The team then repeats the measurements at room temperature to understand how temperature affects the quantum dots’ properties.
The team supplements these practical experiments with computer simulations. “Manufacturing transistors and testing each one individually is expensive and time-consuming,” says undergraduate student Andrei Olar. “So, we also simulate them to test the effects of different changes, using a simulator that considers the quantum effects of individual electrons.” The team then compares the simulation outputs with the results of the practical experiments to see if they agree.
Reference
https://doi.org/10.33424/FUTURUM545
Sorin and the team use the findings from their real and simulated experiments to inform the design of their next transistors, quantum dots and qubit arrays. “We always have new ideas to improve quantum dot performance based on our previous measurements and simulations, and we are inspired by the published findings of other academics in the field,” says Shai. The researchers use these results to update their transistor designs, which are sent back to the foundry. Once manufactured, the new transistors are tested in the lab through cryogenic experiments and computer simulations and the results are used to inform the next designs. Through this iterative process of designing, testing and redesigning, the team is constantly advancing quantum dot technology.
What success has the team had?
In addition to demonstrating that commercially manufactured transistors behave as quantum dots at cryogenic temperatures, the team has also shown it is feasible to create large qubit arrays using commercial semiconductor foundry technologies. Graduate student Suyash Pati Tripathi achieved a significant milestone when he designed the team’s first 2 × 4 quantum dot array. “This breakthrough allowed us to demonstrate the smallest quantum dots (15 nm × 18 nm) that can be coupled to each other – a significant step forward in the field of quantum technology,” he says. “However, that was just the beginning! The next goal is to combine this quantum dot array with electronic circuits to create a fully integrated quantum processor. This integration would bring us closer to developing practical, scalable quantum computers.”
Professor Sorin Voinigescu
The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto, Canada
Fields of research: Quantum engineering, electronics engineering, computer engineering
Research project: Using real and simulated experiments to explore how transistors behave as quantum dots
Funders: Natural Sciences and Engineering Research Council of Canada (NSERC), Ontario Centres of Excellence, Ciena Canada Corporation, EU Horizon 2020 IQubits grant, GlobalFoundries University Partner Program
About quantum engineering
“Quantum engineering blends physics, electronics and computer science to unlock the mysteries of the quantum world, where things behave in ways we don’t yet fully understand but offer incredible potential,” says Suyash. “Not only is quantum engineering intellectually stimulating, but it’s a field where curiosity and creativity are essential.”
Quantum engineers use the principles of quantum physics to develop technologies that have real-world applications. This requires an interdisciplinary approach, combining physics, engineering and computing. “We work at the interface between qubits and electronics,” explains Sorin. “This requires knowledge from quantum physics, semiconductor device and integrated circuit design and development, and computer programming. Without understanding all these areas, you cannot design qubits, qubit arrays or the electronics that control them.”
Quantum engineering is still a relatively new field, as the technologies required to examine and manipulate materials at the nanoscale have not been around for long. This means there are plenty of challenges and opportunities for the next generation of quantum engineers to tackle and embrace. “As a quantum engineer, you’ll be part of a select group shaping the future of technology and innovation,” says Suyash. “As well as helping to solve global challenges, you will redefine what’s possible.”
Pathway from school to quantum engineering
At school and beyond, gain a strong foundation in physics, mathematics and computing.
At university, a degree in quantum engineering, physics, mathematics, computer science or electronics engineering will prepare you for a career in the field. Sorin recommends taking classes in quantum physics, semiconductor devices and circuits, computer programming and architectures, and tensor mathematics.
Learn more about quantum computing from IBM’s free Quantum Learning courses: learning.quantum.ibm.com
Explore careers in quantum engineering
There is a range of careers that use quantum engineering techniques and principles to develop quantum technologies and apply them for practical purposes, from quantum physicists, quantum algorithm programmers and qubit modelling engineers, to semiconductor process engineers, electronic circuit designers and cryogenic engineers.
The Quantum branch of the Institute of Electrical and Electronics Engineers provides educational resources, including articles and videos about quantum physics and technologies: quantum.ieee.org/education
Learn how quantum computing is being used in the real world with IBM’s case studies: www.ibm.com/quantum/case-studies
This article provides a useful guide to careers in quantum computing: www.fastcompany.com/90999848/quantum-computing-careers-explained
Meet the team
Andrei Olar
“I love the physics of quantum engineering. Harnessing something as weird and counterintuitive as quantum mechanics and using it to make something useful – it’s almost like magic! We have lots of questions about what makes a transistor most suitable for using in quantum hardware, and my role in the lab is to simulate the transistors to help answer these questions.”
Shai Bonen
“I love how designing integrated circuits feels like playing video games, but at the end I’ve created something real and physical. And it’s fun to think about how to address the complex problems in quantum computing – it’s a bit like playing strategic board games. Quantum engineering has given me the opportunity to combine my interests and think in fun and exciting ways in a research setting.”
Janelle Frias
“I enjoy the multidisciplinary nature of developing quantum technologies. In physics classes, I always wondered how we could put the puzzling ideas behind quantum physics to use. Now, I appreciate how the interaction between quantum physics and engineering allows me to apply my skills and interests in new and exciting ways.”
Suyash Pati Tripathi
“Studying quantum engineering allows me to transform the fascinating world of quantum mechanics into practical, groundbreaking technology. It feels like uncovering the universe’s hidden principles and turning them into innovations that have the potential to reshape our future. I find great satisfaction in designing quantum computing systems, where abstract concepts from theoretical physics evolve into tangible applications.”
Julie McIntosh
“I enjoy being part of a great team – it’s exciting to work together on big projects and to find creative solutions to challenges. When I was in high school, I never imagined that I would join such a rapidly growing field with important real-world impacts. Now, I study nanoscale devices that may be used to build quantum computers – I am proud of my academic career so far.”
Vivek Dhande
“Quantum engineering is the perfect intersection of the cool weirdness of quantum physics with the application-minded ambitions of engineering. It is exciting to use laws of physics that only occur at the nanoscale to create quantum algorithms that have real-world applications and the potential to change existing industries. Technological hardware is fundamental to this, and this is where quantum engineering happens.”
Do you have a question for the team?
Write it in the comments box below and the team will get back to you. (Remember, researchers are very busy people, so you may have to wait a few days.)
Learn more about the challenges of creating quantum computers:
www.futurumcareers.com/why-is-it-hard-to-build-quantum-computers
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