Teaching: Hands-On

Research Group Webpage Q-Photon
 

Photonic Quantum Computing on a Programmable Silicon Processor:

 

Students operate a real programmable silicon photonic processor — a chip fabricated in a commercial silicon foundry, integrating 264 tunable Mach-Zehnder interferometers on a footprint smaller than a thumbnail — to explore the foundations of linear optical quantum computing. This is not a simulation: students program real hardware using custom control software developed at KTH, inject real single photons from a PPKTP-crystal SPDC source at telecom wavelengths, and detect them with superconducting nanowire single-photon detectors operating at cryogenic temperatures.

Experiments progress from single-qubit control — scanning MZI phases to observe photonic Rabi oscillations and interference fringes — through source characterization via a Hanbury Brown-Twiss g(2)(0) measurement performed directly on the chip, to the culminating Hong-Ou-Mandel experiment. There, two indistinguishable photons meet at a balanced beam splitter and bunch into the same output port, causing coincidence counts to vanish. Students scan the optical delay, observe the HOM dip emerge, and measure its visibility as a direct quantitative benchmark of photon indistinguishability — the fundamental resource that makes photonic quantum computing possible.

 

Courses 

Quantum Photonics Third Cycle FSK3601

Quantum Photonics - Second Cycle SK2900 

WACQT Graduate Course - Third Cycle - Link

 

Quantum Entanglement and Bell Inequality Violation

 

Students generate and characterize polarization-entangled photon pairs using an entanglement demonstrator consisting of a compact optical breadboard housing a blue laser diode, two adjacent type-I BBO down-conversion crystals, fiber couplers, rotating polarizers, and a coincidence counting unit. Students perform a series of experiments that have no classical explanation. Students discriminate between ∣Φ+⟩ and ∣Φ−⟩ by measuring the full coincidence matrix in two bases, before performing a complete CHSH Bell inequality test: 16 coincidence rates across four polarizer-angle combinations, from which students compute the S parameter and its uncertainty from their own data. Quantum mechanics predicts S up to 2 sqrt(2)​; local realism requires S≤2. 

 

Courses 

Quantum Information - Second Cycle SH2381

Optical Physics - Second Cycle SK2303

WACQT Graduate Course - Third Cycle - Link