It seems like a weekly occurrence to hear of the latest huge data hack, exposing vast deposits of customer credit card details, patient records or other sensitive confidential information. This risk of cyber-attack only increases as our world become ever more connected and online, so governments and corporations have sought better ways to secure the information that they send to communicate.
At present, confidential data can be transmitted through fiber-optic cables as flashes of light. This is encrypted, meaning the data is scrambled in a specific way such that a midway interceptor couldn’t understand the message – to decode it requires a digital ‘key’, which is sent alongside. The data and keys are sent as classical bits in 1s and 0s coded through pulses of light, but more advanced hackers can read and duplicate these without leaving any trace.
If we can utilise quantum mechanics in these communication networks, improved security is virtually built-in by the science. Individual particles of light called photons can transmit information as quantum bits called ‘qubits’, in a state of 1, 0 or a bit of both as a ‘superposition’. If an eavesdropper observes these qubits in transit, the quantum state ‘collapses’ back to its classical bit equivalent and hence leaves an obvious sign of uninvited activity.
Quantum key systems transmitting these single photons will require source materials that can finely control the photon quantum properties to be useful. While several materials have been shown to produce single photons on demand such as defects in diamonds, all require extremely low temperatures to operate – almost absolute zero of -273 degrees Celsius – since thermal energy in the system starts to change the quantum states in error as the material warms up and vibrates its lattice in excitement. Scaling up these systems for wider quantum communications networks would be impossible practically, due to cooling costs and other physical considerations.
Very recently, researchers discovered almost by accident that the material hexagonal boron-nitride (hBN) can produce these valuable single photons at gaps in its usual honeycomb atom structure [1]. My work centres on this material, where I’m investigating the light-matter interactions at these nanoscale defects. We use lasers of varying wavelengths to probe hBN’s optical properties in the hope to better understand the different energy states and characteristics of different types, including standalone single defects or larger, brighter ensembles of many.
Previous experiments show tantalising evidence that the optical and quantum properties of hBN might just be good enough to work well close to room temperature [2,3,4], making the idealised concept of quantum networks closer to larger-scale reality. It shows beautifully that in the quantum world, material defects can be unexpected asset.
Credit: Elizabeth Flores-Gomez Murray, Yu Lei and Kazunori Fujisawa.
References:
[1] Tran, et al ‘Quantum emission from hexagonal-boron nitride’, Nature Nanotechnology, 11, 37-41, 2016.
[2] A. Dietrich, et al, ‘Solid-state single photon source with Fourier transform limited lines at room temperature’ Phys Rev B 101 081401 (2020).
[3] H. Stern, et al ‘Room-temperature optically detected magnetic resonance of single defects in hexagonal boron nitride’, Nature Commun. 13 618 (2022).
[4] F.F. Murzakhanov, et al ‘Electron-nuclear coherent coupling and nuclear spin readout through optically polarized VB- spin states in hBN’, ArXiv 2112.10628 (2021).
NanoDTC PhD Student, c2021