Encoding the three flavors of neutrinos will accelerate the work of physicists as they study the collapse of supernovae. (Credit: NASA/DOE/Fermi LAT Collaboration, CXC/SAO/JPL-Caltech/Steward/O. Krause et al., and NRAO/AUI)
In a step forward for both high-energy physics and quantum information science (QIS), an international coalition of researchers has developed quantum algorithms to capture the three flavors of neutrino particles produced during supernova explosions. The team, led by the University of Trento, included experts from the Advanced Quantum Testbed (AQT) at Lawrence Berkeley National Laboratory (Berkeley Lab) and the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy (DOE) Office of Science user facility at Berkeley Lab. This application of QIS will accelerate the work of physicists as they study the collapse of these giant stars and represents a step forward for quantum hardware in the use of many-body problems. Their research was published in Physical Review D in June.
The explosion of supernovae is one way in which all elements in the universe heavier than iron are initially produced. Much of the radiation produced by these explosions comes in the form of neutrinos – particles that play a key role in the formation of the elements. Unique to neutrinos in the supernova environment is collective flavor oscillation, a phenomenon in which, rather than a single particle with a single mass value, any neutrino can take one of three states, or flavors, with three different masses. Because the radiation emitted by a supernova is composed of all three flavors of neutrino, and because the flavor of a particular neutrino can shift from flavor to flavor, measuring the masses of the neutrinos can prove challenging. (Currently, large-scale underground neutrino detectors are being built in the U.S. and other locations around the world to help answer these questions.)
Capturing and encoding the three flavors of neutrino is a compelling application for quantum computing research. Simulating this kind of complex many-body problem, in which many particles interact and dynamically affect each other’s behavior, is an area of physics for which quantum computing is uniquely suited, and tackling it is an opportunity for researchers to develop new quantum methods and hardware.
“Simulating the three flavors of neutrino is a dynamic process, and it’s a quantum many-body process. This is one of those problems that is very hard to do classically – you have to cut corners and do a lot of approximations,” said NERSC quantum computing engineer Ermal Rrapaj, an author on the paper. “But it’s perfect for quantum computing because you can take full advantage of what quantum computers are good for, which is dynamics for many-body systems.”
Complicating the problem, and making it an exciting task for quantum computing engineers, three flavors of neutrino constitute a three-state system. In contrast, the qubits used in quantum computers are two-state systems. To address three-state systems with two-state hardware, researchers have previously used multiple qubits. But in collaboration with AQT, the researchers expanded on AQT’s state-of-the-art research to experiment with three-level quantum hardware, known as qutrits. They developed the first algorithms to allow these measurements to be done using either qubits or qutrits. Ultimately, they found that a scaled-up qutrit device could be ideal for this type of research due to limited overhead and the increased noise tolerance that comes with a larger quantum system.
This work will benefit future researchers by providing the building blocks to run complex, high-energy simulations on quantum computers. It will also provide encoded values for the three flavors of neutrino, enabling scientists to use these encodings for large-scale supernovae simulations when quantum supercomputers become available. As such, this work also indicates where quantum computers in the research space might be headed.
“One key highlight of this project is that we can unlock novel capabilities in these quantum devices, which is not a focus of the commercial quantum computing sector, and the impact of these capabilities in enhancing simulations like these,” said AQT Head of Measurement Ravi Naik. “Exploring these cutting-edge research areas can have huge impacts on the applications that people want to study. So, working beyond what’s out there and commercially available can expose areas where future generations of quantum devices, whether in the academic realm or the industry realm, could have new features. These sorts of research programs highlight the need for that.”
The team’s recent paper represents work on a quantum system with just a few qutrits. But because real-world research using quantum computers will require much larger systems, the next step will be scaling up.
“We did an interesting quantum simulation on a limited-size system,” said Naik. “The problems researchers aim to address with quantum simulation, particularly those with significant impact, involve a vast number of neutrinos, requiring an increase in the scale of our system. A primary focus at AQT is expanding the size of our processors to support the demands of these quantum simulations.”
In the meantime, the researchers say using up-and-coming quantum hardware and methods to address difficult questions in physics is rewarding and opens the door to answers not previously accessible through classical computing methods.
“The exciting part about it was being able to see the hardware and get meaningful physics out of it,” said Rrapaj. “It’s great to see these problems being able to be tackled directly with quantum computers, and people being able to do something they couldn’t do before. There are questions that people had not asked before because they knew it wasn’t possible to solve them in the near term. Now, if you have this capability, what questions can you ask?”
The National Energy Research Scientific Computing Center (NERSC) is the mission computing facility for the U.S. Department of Energy Office of Science, the nation’s single largest supporter of basic research in the physical sciences.
Located at Lawrence Berkeley National Laboratory (Berkeley Lab), NERSC serves 11,000 scientists at national laboratories and universities researching a wide range of problems in climate, fusion energy, materials sciences, physics, chemistry, computational biology, and other disciplines. An average of 2,000 peer-reviewed science results a year rely on NERSC resources and expertise, which has also supported the work of seven Nobel Prize-winning scientists and teams.
NERSC is a U.S. Department of Energy Office of Science User Facility.