In diamonds (and other semiconductor materials), defects are a quantum sensor’s best friend. This is because defects, essentially an arrangement of jostling atoms, sometimes contain electrons with angular momentum, or spin, that can store and process information. This “spinning degree of freedom” can be harnessed for a variety of purposes, such as detecting magnetic fields or creating a quantum network.
Researchers led by Greg Fuchs, Doctor. ’07, a professor of applied and engineering physics at Cornell Engineering, looked for that spin in the popular semiconductor gallium nitride and, surprisingly, found it in two different species of defects, one of which can be manipulated for future quantum applications.
The group’s newspaper.”Optically Detected Single Spin MRI at Room Temperature in GaN”, published on February 12 in Nature Materials. The lead author is PhD student Jialun Luo.
Flaws are what give color to gems, which is why they are also known as color centers. Pink diamonds, for example, get their hue from defects called nitrogen vacancy centers. However, there are many color centers that have not yet been identified, even in commonly used materials.
“Gallium nitride is a mature semiconductor. It has been developed for wide bandgap high-frequency electronics and it has been a very intensive effort for many years,” Fuchs said. “You can go and buy a wafer; you probably have it in your computer charger or electric car. But in terms of material for quantum defects, it hasn’t been explored much.”
To search for the spin degree of freedom in gallium nitride, Fuchs and Luo teamed up with Farhan Rana engineering professor Joseph P. Ripley and doctoral student Yifei Geng with whom they had previously explored the material.
The group used confocal microscopy to identify the defects using fluorescent probes and then performed a series of experiments such as measuring how the fluorescence rate of a defect changes as a function of the magnetic field and using a small magnetic field to drive the resonant spin transmissions of the flaw all at room temperature.
“At first preliminary data showed signs of interesting spin structures but we couldn’t drive the spin resonance,” Luo said. “It turns out that we needed to know the symmetry axes of the defect and apply a magnetic field in the right direction to test for resonances; results brought us more questions waiting to be resolved.”
The experiments showed that the material had two types of defects with different spin spectra. In one case ,the spin was coupled to metastable excited state; in another case,it was coupled to ground state.
In latter case,the researchers were able to see fluorescence changes up-to 30% when they boosted the transition,a large change contrast,and relatively rare ,for spinning quantum at room temperature.
“Usually fluorescence &spin are very weakly coupled so when you change projection ,fluorescence can change by 0 .1 %or something very small,Fuchs said.”From technological point view ,that’s not great,because what you want big change,to measure quickly& efficiently”
The researchers then performed quantum control experiment.They discovered that could manipulate ground state&it had quantum coherence,a quality allows qubits,to retain their information
“That’s something very exciting about this observation,Fuchs said.”There is still lot fundamental work done&more question than answers.But basic discovery,the fact it has strong contrast exists semiconductor material mature opens up all kind possibilities we now excited explore”
The research supported by Cornell Center Material Research(CCMR),with funding National Science Foundation’s Center Material Research Science Engineering program;Cornell Engineering Sprout program;NSF Quantum Sensing Challenges Transformational Advances Quantum Systems program
The researchers made use Cornell Nanoscale Facility also supported NSF.
According to source