16 research outputs found
Hybrid waveguide-bulk multi-path interferometer with switchable amplitude and phase
We design and realise a hybrid interferometer consisting of three paths based
on integrated as well as on bulk optical components. This hybrid construction
offers a good compromise between stability and footprint on one side and means
of intervention on the other. As experimentally verified by the absence of
higher-order interferences, amplitude and phase can be manipulated in all paths
independently. In conjunction with single photons, the setup can, therefore, be
applied for fundamental investigations on quantum mechanics.Comment: accepted in APL Photonic
Totally Destructive Interference for Permutation-Symmetric Many-Particle States
Several distinct classes of unitary mode transformations have been known to
exhibit the strict suppression of a large set of transmission events, as a
consequence of totally destructive many-particle interference. In another work
[Dittel et al., Phys. Rev. Lett. 120, 240404 (2018)] we unite these cases by
identifying a general class of unitary matrices which exhibit such
interferences. Here, we provide a detailed theoretical analysis that
substantially expands on all aspects of this generalisation: We prove the
suppression laws put forward in our other paper, establish how they interrelate
with forbidden single-particle transitions, show how all suppression laws
hitherto known can be retrieved from our general formalism, and discuss
striking differences between bosons and fermions. Furthermore, beyond
many-particle Fock states on input, we consider arbitrary pure initial states
and derive suppression laws which stem from the wave function's permutation
symmetry alone. Finally, we identify conditions for totally destructive
interference to persist when the involved particles become partially
distinguishable.Comment: 16 pages, 4 figure
Totally Destructive Many-Particle Interference
In a general, multi-mode scattering setup, we show how the permutation
symmetry of a many-particle input state determines those scattering unitaries
which exhibit strictly suppressed many-particle transition events. We formulate
purely algebraic suppression laws that identify these events and show that the
many-particle interference at their origin is robust under weak disorder and
imperfect indistinguishability of the interfering particles. Finally, we
demonstrate that all suppression laws so far described in the literature are
embedded in the general framework that we here introduce.Comment: 6 pages, 2 figure
Indistinguishability of identical bosons from a quantum information theory perspective
Using tools from quantum information theory, we present a general theory of
indistinguishability of identical bosons in experiments consisting of passive
linear optics followed by particle number detection. Our results do neither
rely on additional assumptions on the input state of the interferometer, such
as, for instance, a fixed mode occupation, nor on any assumption on the degrees
of freedom that potentially make the particles distinguishable. We identify the
expectation value of the projector onto the -particle symmetric subspace as
an operationally meaningful measure of indistinguishability, and derive tight
lower bounds on it that can be efficiently measured in experiments. Moreover,
we present a consistent definition of perfect distinguishability and
characterize the corresponding set of states. In particular, we show that these
states are diagonal in the computational basis up to a permutationally
invariant unitary. Moreover, we find that convex combinations of states that
describe partially distinguishable and perfectly indistinguishable particles
can lead to perfect distinguishability, which itself is not preserved under
convex combinations