By peering into the hearts of diamonds, scientists at the Penn Center for Quantum Information, Engineering, Science and Technology (Penn QUIEST) are developing new quantum-based sensor technologies that could revolutionize materials, chemistry, biology and medicine and data science.
The key to their work lies in finding novel methods that can sense and manipulate the quantum properties that underlie all of nature, focusing on the quantum property called “spin.”
Spin is essentially a magnetic moment within a subatomic particle, which can point up, down or any direction in between, and changes as it’s perturbed by its environment. One method to sense spin involves firing lasers at flaws in the crystalline structure of a diamond. A diamond is mostly comprised of a regular arrangement of carbon atoms, but sometimes a stray element sneaks in, or a carbon atom goes missing. This can create a nitrogen vacancy (NV) center, with a nitrogen atom sitting next to an empty slot where a carbon atom should be, and the resulting NV center can be used to sense the spin of electrons. These “quantum sensors” have enormous potential.
Quantum Sensing
When a laser is fired into an NV center, the brightness of the light coming out changes depending on the spin. Treating a tiny sliver of man-made diamond, or nanodiamond, with chemicals will cause it to attach to a particular molecule of interest, such as a protein in a blood sample, and light up in a specific way. This technique provides a more sensitive, longer-lasting tag than those currently in use to identify molecules for diagnostic tests and biological research.
While such tags have long been important in those areas, quantum sensors have other uses as well. “These electron spins are so sensitive that they can actually detect the presence and the dynamics of other individual atoms,” says Lee C. Bassett, Associate Professor in Electrical and Systems Engineering and the inaugural director of Penn QUIEST. “As soon as you have the ability to measure something that you couldn’t before, it opens up all sorts of possibilities.”
For instance, many molecules have structures that aren’t well understood. Quantum sensing could allow researchers to examine those structures and gain insight into the basic physics of certain materials or suggest how they’d respond to changes in their environment. In turn that could yield new battery chemistries, for example, or create alloys with previously unavailable properties.
Qubit Possibilities
Diamonds hold other quantum potential as well. Most of a diamond’s atoms are carbon-12, which have zero spin and can’t be manipulated with a magnetic field. About 1 percent, though, are carbon-13 atoms, which do respond to a magnet. These carbon-13 atoms could act as quantum bits, or “qubits.” Qubits can be in superposition; their spins can point up, down, or in another direction simultaneously.
Because they provide more simultaneous state possibilities than the simple 0/1, off/on state of bits in traditional computing, those overlapping spin states allow quantum computers to perform multiple calculations at the same time and much faster than classical computers. They might, for instance, simulate chemical reactions that are too complicated for a traditional computer to handle. Bassett and his colleagues are working on ways to manipulate and read out the qubits, including a so-called “meta-lens” that can capture light shined through the qubits and send it into optical fiber for easier viewing.
Diamonds hold other quantum potential as well. Most of a diamond’s atoms are carbon-12, which have zero spin and can’t be manipulated with a magnetic field. About 1 percent, though, are carbon-13 atoms, which do respond to a magnet. These carbon-13 atoms could act as quantum bits, or “qubits.” Qubits can be in superposition; their spins can point up, down, or in another direction simultaneously.
Spin states can also be “entangled” so measuring spin in one reveals the spin in another, even if the two atoms are far apart. This has implications for improving the strength of sensors. Using 100 classical sensors only improves the sensitivity by 10 times; using 100 entangled sensors would be 100 times more sensitive than one sensor. These entangled sensors might, for instance, be able to see the changes in a single molecule as it binds or unbinds with another. And because of the ability to transmit information between widely separated qubits, entanglement could also be key to speeding quantum information processing and communication even further.
Expanding Capabilities
Diamonds are just one of the materials that the Center’s researchers are leveraging for their work. They are also working with hexagonal boron nitride, an atomically thin arrangement of atoms that can also include atomic vacancies similar to the NV centers found in diamonds, but that might provide even greater sensitivity than those diamonds.
Penn QUIEST is also part of a consortium working on yet another quantum material, quantum dots, the technology that won the 2023 Nobel Prize in Chemistry. Quantum dots can be made to be more uniform than diamonds, allowing the dots to work better as sensors or qubits.
Eventually, Bassett hopes the Center can achieve for its sensor and other research areas what scientists call “quantum advantage,” which is when a quantum mechanical system can do something a classical system can’t, as quantum computing hopes to do. Where that will happen first is hard to predict, but it could be in Penn QUIEST. “There is huge potential for quantum sensing applications in biomedical technologies alone,” says Bassett. “There’s a real opportunity for us to fundamentally change how many scientific fields do their work.”