Original title: Spin-to-polarization mapping with a coherent quantum dot-cavity receiver
Adrià Medeiros, Vincent Vinel, Eliott Rambeau, Petr Steindl +11 · September 2026
Quantum computers need reliable ways to connect light particles, called photons, to fixed memory bits called qubits. To build reliable quantum gates, the polarization of a bouncing photon—which is the direction its light waves wiggle—must match the state of a qubit perfectly. Researchers tested this match using a tiny semiconductor crystal, known as a charged quantum dot, trapped inside a miniature pillar cavity. They bounced photons off the system. Detecting just one bounced photon set the trapped electron's spin into a specific state with 95±2% fidelity. A second bounced photon let them track the spin relaxing. Once a brief initial delay passes, each spin state produces a distinct, opposite polarization. This shows an electron spin can directly shape a photon's polarization.
Imagine you have a sealed jar of cookies that is either oatmeal raisin or chocolate chip, and you want to know which without opening it. You drop a small ball into the jar; the sound it makes when hitting the cookies tells you the cookie type. In this paper, they send a photon into a tiny structure, and the polarization of the reflected photon—like the sound—directly indicates the spin state of an electron inside. One photon measurement is enough to know the spin, just as one sound tells you the cookie type.
This mapping is crucial for building reliable quantum computers and networks, where photons and spins need to be perfectly linked to perform calculations. Without such a one-to-one correspondence, quantum operations would be error-prone and slow.
The results are limited by a competition between the electron spin relaxation time and the trion radiative lifetime. The demonstration is an experimental signature, not a full logical gate.
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Spin-to-polarization mapping with a coherent quantum dot-cavity receiver — Adrià Medeiros, Vincent Vinel, Eliott Rambeau et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.