Scientists Just Made ‘Biological Qubits’ That Act as Quantum Sensors Inside Cells

Fragile quantum states might seem incompatible with the messy world of biology. But researchers have now coaxed cells to produce quantum sensors made of proteins.

Quantum states are incredibly sensitive to changes in the environment. This is a double-edged sword. On the one hand, they can sense physical properties with unprecedented precision. At the same time, they’re extremely delicate and hard to work with.

This sensitivity makes it challenging to create quantum sensors that work in living systems, which are warm, biochemically active, and in constant motion. Scientists have tried to integrate various kinds of synthetic quantum sensors into biology, but they’ve been bedeviled by problems related to targeting, efficiency, and durability.

Now, a team from the University of Chicago says they’ve repurposed fluorescent proteins used for biological imaging into quantum sensors that operate inside cells. These proteins can be encoded in DNA so the cells produce the sensors themselves, allowing the devices to target sub-cellular structures.

“Our findings not only enable new ways for quantum sensing inside living systems but also introduce a radically different approach to designing quantum materials,” Peter Maurer at the University of Chicago, who helped lead the research, said in a press release.

“We can now start using nature’s own tools of evolution and self-assembly to overcome some of the roadblocks faced by current spin-based quantum technology.”

Fluorescent proteins are already widely used for biological imaging. They can be tagged onto target proteins for an optical readout of where that protein is expressed in the cell. In a paper in Nature, the researchers note that it was already known many of these proteins exhibit a quantum state called a triplet state, but no one had tried to make them into quantum sensors.

The researchers realized this triplet state could be used as a qubit to store quantum information. More importantly, the state could be read optically using a special microscope. These qubits could potentially measure things like magnetic and electrical fields deep inside cells.

“Rather than taking a conventional quantum sensor and trying to camouflage it to enter a biological system, we wanted to explore the idea of using a biological system itself and developing it into a qubit,” said David Awschalom at the University of Chicago, who helped lead the research.

In their study, the researchers focused on a particular yellow fluorescent protein. After confirming they could read out its quantum state at extremely cold temperatures, they then demonstrated they could also make readouts when the protein was expressed in mammalian cells.

In the future, such a quantum sensor could carry out magnetic resonance imaging, or MRI, at the scale of individual cells. This could make it possible to reveal the atomic structure of cellular machinery or even investigate how drugs bind to specific proteins inside the cell. In a test along these lines, the researchers expressed the fluorescent protein in bacterial cells and showed it could be used to detect the presence or absence of a magnetic field.

Actually making it into a useable quantum sensing platform would require significant improvements in stability and sensitivity, say the researchers, as well as new quantum sensing techniques. Still, it has the potential to provide a powerful new lens in the study of biology.

“Through fluorescence microscopy, scientists can see biological processes but must infer what’s happening on the nanoscale,” says Benjamin Soloway at the University of Chicago, one of the lead authors of the new paper. “Now, for the first time, we can directly measure quantum properties inside living systems.”