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Quantum state characterization and state engineering using photon-number-resolving measurements

February 28, 2020 - 12:00pm
Rajveer Nehra
University of Virginia, Charlottesville, VA

(pizza and drinks served at 12pm; talk starts at 12:10pm)

We are in the midst of a second quantum revolution fueled by the
remarkable quantum mechanical properties of physical systems.
Therefore, characterization and engineering of these quantum systems
is vitally important in emerging quantum optical science and
technology. The Wigner quasi-probability distribution function
provides such a characterization. First, we present our recent results
on quantum state tomography of a single-photon Fock state by
photon-number-resolving (PNR) measurements using superconducting
transition-edge sensor [1].
We directly probe the negativity of the Wigner function in our raw
data without any inference or correction for decoherence, which is
also an important indicator of the “quantum-only” nature of a physical
system. Next, we introduce and experimentally demonstrate a state
characterization protocol by measuring the Wigner function overlap
between the unknown state and a sufficiently large set of readily
available coherent state probes [2]. Unlike conventional continuous
variable state tomography methods, our method utilizes computationally
efficient semi-definite programming and can be used to accurately
reconstruct the state even after loss a known loss. The protocol is
demonstrated for a weak coherent state and a single-photon Fock state,
and is shown to be robust to experimental noise.
Towards the end, we discuss about ongoing experiment for generating
non-Gaussian states using a process known as photon catalysis which
involves coherent states, single-photon states, linear optics, and PNR
measurements [3].

[1] R. Nehra et al., Optica 6,1356–1360 (2019). [2] R. Nehra et al.,
arXiv:1911.00173v1. [3] M. Eaton et al., N.J.Phys. 21, 113034 (2019)

ATL 2324