Publications [#348127] of Iman Marvian

Papers Published
  1. I. Marvian, R. W Spekkens, No-Broadcasting Theorem for Quantum Asymmetry and Coherence and a Trade-off Relation for Approximate Broadcasting, Physical Review Letters (July, 2019), pp. 020404 [PhysRevLett.123.020404], [doi] .

    Abstract:
    Symmetries of both closed- and open-system dynamics imply many significant constraints. Thesegenerally have instantiations in both classical and quantum dynamics (Noether’s theorem, for instance,applies to both sorts of dynamics). We here provide an example of such a constraint which has nocounterpart for a classical system, that is, a uniquely quantum consequence of symmetric dynamics.Specifically, we demonstrate the impossibility of broadcasting asymmetry (symmetry breaking) relative toa continuous symmetry group, for bounded-size quantum systems. The no-go theorem states that if twoinitially uncorrelated systems interact by symmetric dynamics and asymmetry is created at one subsystem,then the asymmetry of the other subsystem must be reduced. We also find a quantitative relation describingthe trade-off between the subsystems. These results cannot be understood in terms of additivity ofasymmetry, because, as we show here, any faithful measure of asymmetry violates both subadditivity andsuperadditivity. Rather, they must be understood as a consequence of an (intrinsically quantum)information-disturbance principle. Our result also implies that if a bounded-size quantum reference framefor the symmetry group, or equivalently, a bounded-size reservoir of coherence (e.g., a clock withcoherence between energy eigenstates in quantum thermodynamics) is used to implement any operationthat is not symmetric, then the quantum state of the frame or reservoir is necessarily disturbed in anirreversible fashion, i.e., degraded.

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