Lillian Hughes, a graduate student in the PRL department, has had a big hand in developing a new approach to quantum sensing. Her research interests include engineered defects in diamonds, known as spin qubits. Working alongside Ania Jayich, a leading figure in quantum science and co-director of UC Santa Barbara’s National Science Foundation Quantum Foundry, Hughes has successfully demonstrated a groundbreaking method of arranging and entangling two-dimensional ensembles of defects within diamond for the first time.
The research is based on the properties of nitrogen-vacancy (NV) centers in diamond with long-lived spin states. These properties make NV centers particularly well-suited for quantum sensing applications. Hughes’ work is the engine behind entanglement-assisted sensing that strengthens the signals we’re looking for without scaling up the noise—the key to making better and more precise measurements.
Jayich’s lab mainly uses lab-grown diamonds as a platform to investigate the use of spin qubits in quantum sensing applications. She also points out just how important the spin degree of freedom is. It’s as simple and elegant as magnetic resonance imaging (MRI) sensors are powerful.
“Nuclear magnetic resonance [NMR] is based on detecting very small magnetic fields coming from the constituent atoms in, for example, biological systems.” – Ania Jayich
Hughes has collaborated with Jayich on two additional co-authored papers. Their studies, including one in Physical Review X and two in Nature, detail their groundbreaking efforts. The study describes a scheme to “squeeze” noise amplitude by inducing correlations between the particles to generate a spin-squeezed state. This technique is perhaps the most important for raising any potential metrological gain to account—effectively amplifying signal strength without the addition of new noise.
One of the best ways to do this metrological gain, Jayich notes, is through the manipulation of spin arrangement. For this, he zeroes in on the two-dimensional plane. As she explains, a big materials challenge comes from the random incorporation of spins throughout the structure of the diamond.
“There’s a materials challenge here, in that, because we can’t dictate exactly where the spins will incorporate, they incorporate in somewhat random fashion within a plane.” – Ania Jayich
She goes on to explain that tackling this challenge is key to achieving real world quantum advantage in sensing. Hughes continued to explain how they have been able to produce arrays of NV center spins with very specific density and dimensionality in a controlled manner.
“We can create a configuration of nitrogen-vacancy (NV) center spins in the diamonds with control over their density and dimensionality, such that they are densely packed and depth-confined into a 2D layer.” – Lillian Hughes
These areas, and particularly the development of more sensitive quantum magnetic field sensors, stand to be transformed by this novel research through enhanced measurement sensitivity and precision. Jayich is cautiously confident that technical challenges will be overcome to show a quantum advantage in practical sensing experiments in the near future.
“What’s new here is that, because Lillian was able to grow and engineer these very strongly interacting dense spin ensembles, we can actually leverage the collective behavior, which provides an extra quantum advantage.” – Ania Jayich