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This work delves into the classification of beamsplitters within the regimes of bosonic and fermionic models. It defines universal beamsplitters as those that can densely generate SU(m) or SO(m) on m modes. Real beamsplitters have been established to be universal for three or more modes, while the potential universality of complex beamsplitters on the same condition is explored. The text also addresses important open questions regarding the proof of universality, extensions to multi-mode systems, and the implications of phase applications in beamsplitter operations.
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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?