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Classifying Beamsplitters. Adam Bouland. Boson/Fermion Model. M modes. Boson/Fermion Model. Boson/Fermion Model. Beamsplitters. Def: A set of beamsplitters is universal if it densely generates SU(m) or SO(m) on m modes. Beamsplitters.
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Classifying Beamsplitters Adam Bouland
Boson/Fermion Model M modes
Beamsplitters • Def: A set of beamsplitters is universal if it densely generates SU(m) or SO(m) on m modes.
Beamsplitters • Def: A set of beamsplitters is universal if it densely generates SU(m) or SO(m) on m modes. Q: Which sets of beamsplitters are universal?
Beamsplitters • Obviously not universal:
Beamsplitters • Obviously not universal: • Not obvious:
Real Beamsplitters Thm: [B. Aaronson ’12] Any real nontrivial beamsplitter is universal on ≥3 modes.
Real Beamsplitters Thm: [B. Aaronson ’12] Any real nontrivial beamsplitter is universal on ≥3 modes. What about complex beamsplitters?
Complex Beamsplitters Goal: Any non-trivial (complex) beamsplitter is universal on ≥3 modes.
Complex Beamsplitters Goal: Any non-trivial (complex) beamsplitter is universal on ≥3 modes. Can show: Any non-trivial beamsplitter generates a continuous group on ≥3 modes.
Complex Beamsplitters Determinant ±1
Complex Beamsplitters Let G=<R1,R2,R3>
Complex Beamsplitters Subgroups of SU(3): 6 infinite families 12 exceptional groups
Complex Beamsplitters Subgroups of SU(3): 6 infinite families 12 exceptional groups
Complex Beamsplitters Let G=<R1,R2,R3> Lemma: If G is discrete, R1,R2,R3 form an irreducible representation of G.
Complex Beamsplitters Δ(6n2)
Complex Beamsplitters Δ(6n2) Algebraic Number Theory
Open questions • Can we complete the proof to show any beamsplitter is universal? • Can we extend this to multi-mode beamsplitters? • What if the beamsplitter applies a phase as well?