14th SmoleQ Greeting Seminar (2025.12.15 at 17:00 (JST))

 

Speaker: 

Shinichi Saito

Research & Development Group, Hitachi, Ltd., Tokyo 185-8601, Japan.

Title: 

Why Micro is different from Macro?
A Challenge towards Macroscopic Quantum Technologies

Abstract:

We consider why microscopic quantum mechanics seems to be different from macroscopic classical mechanics by using coherent photons emitted from a standard laser source. The coherent states describe quantum states of macroscopic number of photons, paving a way to realise macroscopic quantum technologies.  We developed an SU(N) representation theory to describe both spin and orbital angular momentum of coherent photons and experimentally demonstrated their controls over a full Poincaré sphere. We found Stokes parameters are spin expectation values by SU(2) wavefunctions, which exhibit non-trivial topological features like a torus, a Möbius strip, and a bosonic Dirac cone. We also ascribed topological colour charge to photonic orbital angular momentum, whose SU(3) states are shown on a Gell-Mann hypersphere in SO(8). We also realised photonic SU(4) states of singlet and triplet states, which were successfully projected into SU(2)×SU(2) states by a rotated polariser.Finally, we would like to discuss the recent demonstration of CNOT operation using coherent photons and conversion from a photonic skyrmion to an anti-skyrmion through SU(6) symmetry.