In Building 13 on the MIT campus is a half-million-dollar piece of equipment that looks like a long, stretching chandelier, with a series of gold discs connected by thin silver tubes. The equipment, known as a dilution refrigerator, is a major player in doctoral student Alex Greene’s research, incorporating all of their experiments. They say: “My life is shaped around its rhythms.”
The first time Green helped put fresh samples in the freezer, they were working with a postdoc at midnight on Friday, streaming Danish scream music. Since then, the refrigerator has led them on both exciting and frustrating adventures during their PhD research on reducing errors in quantum computing systems.
Green grew up in northern New Jersey with their identical twin Jimmy. The two were very competitive when they were kids, and outside of school, they kept themselves busy by 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 laboratory known for pioneering key technology for computers and phones.
In 2010, Alex and Jamie came to MIT as undergraduates. Alex was interested in biomedical engineering during high school, “but then I found out that I hate working in ‘wet’ labs, where scientists deal with chemical and biological materials, they say. Another influence was ‘Contact’ by Carl Sagan, a science fiction book about a scientist “It got me into physics,” says Green.
As an undergraduate student at MIT, Green majored in physics, 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 physics concepts in quantum mechanics.
Green remained at the Massachusetts Institute of Technology to pursue an MA in quantum computing, where he worked at the Lincoln Laboratory. There, they looked for ways to improve a technology called trapping ion quantum computing, which uses atoms suspended in the air and controlled by a laser.
After completing their master’s, they focused on a different technology called superconducting quantum computing. Instead of suspended atoms, this technology uses exceptionally small electrical circuits to carry electric current. To control these circuits, researchers only need to send electrical signals.
For this project, Green wanted to work with MIT professor William Oliver, who directs the Center for Quantum Engineering at the Electronics Research Laboratory. Once again, Green chose to remain at the institute – this time to pursue a Ph.D.
Adding randomness to quantum computers
One day, quantum computers may solve problems beyond the reach of ordinary classical computers, allowing tremendous advances in many applications. However, manipulating devices so that they show quantum behavior is challenging from a technological perspective. Currently, quantum computers, including superconducting ones, face high error rates that limit the length and complexity of the “programs” they can run. Most empirical research in quantum computing focuses on addressing these errors.
Greene is making superconducting quantum computers more accurate by reducing the impact of these errors. To test their ideas, they need to conduct experiments on superconducting circuits. But for these circuits to work, they must be cooled to extremely low temperatures, about -273.13 degrees Celsius – within 0.02 degrees away from the coldest possible temperature in the universe.
This is where the chandelier-like dilution refrigerator comes into play. The refrigerator can easily reach the required cold temperatures. But sometimes he misbehaves, sending Greene on side missions to fix his problems.
Greene’s grueling side quest involved chasing a leak in one of the refrigerator tubes. The tubes carry a rare and expensive gaseous mixture used to cool the refrigerator, which Green cannot afford to lose. Fortunately, even with the leak, the refrigerator is designed to keep running without losing any mixture for about two weeks at a time. But to keep the refrigerator in service, Greene had to turn it back on and clean it constantly over the course of five days. After nearly seven grueling months, Green and his lab colleague located the leak and repaired the leak, allowing Green to resume their research at full speed.
To strategize how to effectively improve the accuracy of superconducting quantum computers, Greene first needed to evaluate the different types of errors in these systems. In quantum computing, there are two categories of errors: incoherent and coherent errors. Non-coherent errors are random errors that occur even when the quantum computer is idle, while coherent errors occur due to incomplete control of the system. In quantum computers, correlative errors are often the worst cause of system inaccuracies; The researchers showed mathematically that coherent errors accumulate much faster than incoherent errors.
To avoid the bad compound errors of coherent errors, green used a clever tactic: camouflaging these errors to appear as incoherent errors. “If you are [strategically] Incorporating a bit of randomness into superconducting circuits, “You can get coherent errors that accumulate slowly like incoherent errors, they say. Other researchers in the field also use randomness tactics in different ways. However, through their research, Green helps with Paving the way for more accurate superconducting quantum computers.
Improving water sanitation in Pakistan
Outside of research, Green is constantly engulfed in a whirlpool of activities, adding new hobbies while painstakingly removing old ones to make room in their busy schedule. Over the years, their hobbies have included glassblowing, singing in a local queer choir, and competitive rock climbing. Currently, they spend their weekends working on home improvement projects with their rainbow collaboration partner.
Over the past year and a half, Greene has also been involved in classroom water sanitation projects with MIT D-Lab, a project-based program aimed at helping poor communities around the world. Taking classes at D-Lab was “something I’ve always wanted to do from a college student but never had time for,” they say. They were finally able to fit the D-Lab into their schedule using classes to help meet their Ph.D. requirements.
For one project, they are developing a system to effectively and cheaply filter excess harmful fluoride from Pakistan’s water supply. They say, “It doesn’t make sense that fluoride is harmful because we have fluoride in our toothpaste.” “But in reality, too much fluoride alters the hardness of your teeth and bones.” One idea they and their collaborators are exploring is to build a water purification system using clay, a well-established but inexpensive method for removing fluoride.
A visiting assistant professor from Pakistan, who was participating in the D-Lab class, had originally pitched the Fluoride Filtration Project. When the class ended, the professor returned to Pakistan but continued with the project. Greene is now virtually working with the professor to help figure out the best type of clay to filter out fluoride. Through their experiences with D-Lab, Greene sees them continue to volunteer for water sanitation projects over the long term.
Green plans to finish his Ph.D. in December. After 12 years at MIT, Green aims to leave the institute to work for a quantum computing company. “It’s a really great time to be in the industry” in the industry, they say. Companies start to expand [quantum computing] technology.”