“Key step in the integration of quantum-diamond sensors with CMOS technology”
For the first time scientists have created a quantum sensor on a silicon chip; a milestone that may mark a path towards economically viable quantum sensors and computing hardware.
Researchers at MIT have fabricated the sensors from a diamond base. Diamonds, a solid form of carbon, contain nitrogen-vacancy centres which can be affected by light and microwaves. When manipulated, these defects in the diamond emit coloured photons that can convey quantum information about magnetic and electric fields in their proximity.
Nitrogen-vacancy-based quantum sensors already exist, but they are the size of a table and cannot be practically integrated into devices. MIT has managed to scale down the system, which contains optical filters, photodetectors and a microwave generator, down to the millimetre-scale, via semiconductor fabrication techniques.
The ability to detect a magnetic field’s strength, direction and any changes pertaining to that field allows researchers to develop devices that can be used for neuroimaging, biosensing and object detection.
Christopher Foy, a graduate student in the Department of Electrical Engineering and Computer Science at MIT and co-author on a paper about the quantum sensors commented in a blog that: “It’s very difficult to block magnetic fields, so that’s a huge advantage for quantum sensors. If there’s a vehicle traveling in, say, an underground tunnel below you, you’d be able to detect it even if you don’t see it there.”
Quantum Sensor Chip Architecture
The fabrication of the chip is made possible due to nitrogen-vacancy centres. Diamonds have an atomic crystal cube structure that consists of 8 carbon atoms. A nitrogen-vacancy centre is created when two adjacent carbon atoms are removed and replaced by a nitrogen atom and a vacant space.
This vacant space results in missing bonds within the diamond structure, this causes electrons to become hyper sensitive to any variation in magnetic or electrical fields close to the diamond.
The nitrogen-vacancy centre in the diamond has ‘photoluminescent properties,’ put simply it will absorb and emit photons of different colours. Researchers can measure the different colours, in particular the amount of red photons, to gleam quantum insight about the manipulated structures environment.
To do this traditionally you normally need a mounted laser, power supply, conductors and a microwave generator to name but a few of the expensive and cumbersome components. Instead the MIT researchers have used complementary metal-oxide-semiconductor technology to build a chip architecture that stacks small and cheap components to create a complex 3D structure on a chip.
Ron Walsworth, a senior lecturer at Harvard University an independent Nitrogen-vacancy centres researcher commented: “They have taken a key step in the integration of quantum-diamond sensors with CMOS technology, including on-chip microwave generation and delivery, as well as on-chip filtering and detection of the information-carrying fluorescent light from the quantum defects in diamond.
“The resulting unit is compact and relatively low-power. Next steps will be to further enhance the sensitivity and bandwidth of the quantum diamond sensor [and] integrate the CMOS-diamond sensor with wide-ranging applications, including chemical analysis, NMR spectroscopy, and materials characterization.”