Fascinating technology

Making Quantum Computers More Accurate | MIT News

In Building 13 on the MIT campus, there is a half-million-dollar piece of equipment that looks like a long, elongated chandelier, with a series of gold discs connected by thin silver pipes. The equipment, known as the Dilution Refrigerator, is a key part of PhD student Alex Greene’s research, as it houses all of their experiments. “My life is shaped around its rhythms”, they say.

The first time Greene helped put new samples in the fridge, they were working with a postdoc at midnight on a Friday, blasting out Danish shouto music. Since then, the refrigerator has taken them on both exciting and frustrating adventures throughout their doctoral research on error reduction in quantum computing systems.

Greene grew up in northern New Jersey with their identical twin, Jamie. Both were extremely competitive as children, and outside of school they kept busy running, pole vaulting, and rock climbing. Their father is a neurologist and their mother is a former electrical engineer who worked at Bell Labs, a research lab known for pioneering key technology for computers and phones.

In 2010, Alex and Jamie both arrived at MIT as undergraduate students. Alex had become interested in biomedical engineering in high school, “But then I discovered that I hated working in ‘wet’ labs, where scientists handle chemicals and biological materials, they say. Another influence was Carl Sagan’s “Contact,” a science fiction book about an astronomer in search of extraterrestrial intelligence. “It got me hooked on physics,” says Greene.

As an undergraduate at MIT, Greene earned a double major in physics and electrical engineering and computer science. They have found a home in the field of quantum computing, where researchers are working to build extremely powerful computers by taking advantage of the physical concepts of quantum mechanics.

Greene stayed at MIT to pursue a master’s degree in quantum computing, working at Lincoln Laboratory. There they researched ways to improve a technology called trapped ion quantum computing, which uses atoms suspended in air and controlled by lasers.

After completing their masters, they turned to a different technology called superconducting quantum computing. Instead of airborne atoms, this technology uses tiny electric circuits that are exceptional at carrying electric current. To control these circuits, the researchers only have to send electrical signals.

For this project, Greene wanted to work with MIT professor William Oliver, who directs the Center for Quantum Engineering at the Electronics Research Laboratory. Once again Greene chose to stay at the Institute, this time to pursue his doctorate.

Adding randomness to quantum computers

One day, quantum computers could solve problems beyond the scope of normal classical computers, enabling immense advances in many applications. However, manipulating the material to exhibit quantum behavior is challenging from a technological perspective. Currently, quantum computers, including superconducting ones, struggle with high error rates that limit the length and complexity of the “programs” they can run. Most experimental research in quantum computing focuses on solving these errors.

Greene is working to make superconducting quantum computers more accurate by reducing the impact of these errors. To test their ideas, they must conduct experiments on superconducting circuits. But for these circuits to work, they must be cooled to extremely low temperatures, around -273.13 degrees Celsius, within 0.02 degrees of the coldest possible temperature in the universe.

That’s where the chandelier-shaped dilution refrigerator comes in. The refrigerator can easily reach the required cold temperatures. But sometimes he misbehaves, sending Greene on side quests to solve his problems.

Greene’s toughest side quest involved looking for a leak in one of the refrigerator pipes. The pipes carry an expensive and rare gas mixture used to cool the refrigerator, which Greene could not afford to lose. Luckily, even with the leak, the fridge was designed to stay functional without losing mix for about two weeks at a time. But, to keep the refrigerator running, Greene had to constantly restart and clean it during a five-day process. After about seven stressful months, Greene and his lab mate finally located and repaired the leak, allowing Greene to resume his research at full speed.

To develop a strategy to effectively improve the accuracy of superconducting quantum computers, Greene first needed to take stock of the different types of errors in these systems. In quantum computing, there are two categories of errors: inconsistent errors and consistent errors. Inconsistent errors are random errors that occur even when the quantum computer is idle, while consistent errors are caused by imperfect control of the system. In quantum computers, consistent errors are often the worst culprits of system inaccuracies; researchers have mathematically shown that consistent errors accumulate much faster than inconsistent errors.

To avoid nasty inaccuracies made up of consistent errors, Greene employed a clever tactic: disguising those errors to make them look like inconsistent errors. “If you [strategically] introduce some randomness into superconducting circuits,” they say. Other researchers in the field also use random tactics in different ways, Greene notes. Nonetheless, through their research, Greene is helping to pave the way for more accurate superconducting quantum computers.

Improving water sanitation in Pakistan

Outside of research, Greene is constantly engaged in a flurry of activity, adding new hobbies while painstakingly removing old ones to make room in his busy schedule. Over the years, their hobbies have included glass blowing, singing in a local queer choir, and competitive rock climbing. Currently, they spend their weekends working on home improvement projects with their partner in their rainbow-colored co-op.

Over the past year and a half, Greene has also been involved in water sanitation projects through classes with the MIT D-Lab, a project-based program aimed at helping impoverished communities around the world. . Taking classes at D-Lab was “something I always wanted to do since undergrad, but never had time for it,” they say. They were eventually able to fit D-Lab into their schedule by using the courses to meet their PhD requirements.

For one project, they are developing a system to efficiently and cost-effectively filter harmful excess fluoride from water supplies in Pakistan. “It’s not intuitive that fluoride is bad because we have fluoride in our toothpaste,” they say. “But in fact, too much fluoride changes the hardness of your teeth and bones.” One idea they and their collaborators are exploring is to build a water filtration system using clay, an established but inexpensive fluoride removal method.

A visiting assistant professor from Pakistan, who participated in the D-Lab class, originally presented the fluoride filtration project. At the end of the course, the professor returned to Pakistan, but still continued with the project. Greene is now working virtually with the professor to help determine the best type of clay to filter out fluoride. Through their experiences with D-Lab, Greene sees herself continuing to volunteer on long-term water remediation projects.

Greene plans to complete her doctorate in December. After 12 years at MIT, Greene aims to leave the institute to work at a quantum computing company. “It really is a great time to be on the ground” in the industry, they say. “Businesses are starting to grow [quantum computing] Technology.”