A University of North Carolina at Chapel Hill research team has demonstrated a novel way to encode quantum information directly within the light produced by two-dimensional perovskites - opening a potential path to simpler, more efficient quantum communication systems. The study explores how spin dynamics in two-dimensional organic–inorganic hybrid perovskite (2D-OIHP) quantum wells can generate polarization-encoded photons suitable for secure communication protocols.
Two-dimensional perovskites are well known for their performance in light-emitting and photovoltaic devices, but the UNC team, led by Professor Andrew Moran, has shown they can also act as microscopic light sources whose intrinsic exciton spin behavior defines the polarization of emitted photons. When ultrafast laser pulses excite the material, they generate pairs of bound charge carriers - excitons - whose spins determine the polarization of emitted light.
By tracking these spin-dependent polarization changes on femtosecond timescales using four-wave mixing spectroscopy, the researchers revealed that the emitted light transitions from elliptical to linear polarization as exciton spins relax. This natural switch provides two distinct photon states that can be used to encode binary information. “That difference gives us two clearly distinguishable photon states, which is exactly what we need to encode digital information,” explained lead author and Ph.D. researcher Zijian Gan.
Crucially, the team identified that biexciton correlations - interactions between two excitons within the same quantum well - significantly amplify the emitted signal and enhance polarization contrast. According to co-lead author Shuyue Feng, this effect allows information transmission using far fewer photons than typical methods. In some tests, only about 10 photons were required to send a single binary bit, demonstrating a substantial improvement in transmission efficiency.
To put the concept into practice, the group implemented the BB84 quantum key distribution (QKD) protocol using the polarization states of photons emitted by their 2D-OIHP sample. Instead of relying on external optical modulators or wave plates to define polarization, the encoded photon states emerged directly from the material’s electronic structure and spin relaxation processes. As a proof of concept, the team successfully transmitted a short ASCII message - an eight-character phrase totaling 56 bits - through the perovskite system.
“This shows that the material’s internal physics can actually perform part of the job that normally requires complicated optical equipment,” said Moran. The findings suggest that the nonlinear optical processes intrinsic to layered perovskites could generate polarization-encoded photons on demand, providing a compact, material-based route to secure photon sources for future quantum networks.
Looking ahead, the Moran Lab is exploring whether similar spin-control mechanisms can be achieved in related semiconductor and quantum dot systems. For now, the work establishes two-dimensional hybrid perovskites as a versatile platform where spin-dependent nonlinear optical phenomena can be directly harnessed for next-generation quantum communication technologies.