Quantum Optics Seminar by Maria Fuwa – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Maria Fuwa

Historically, two complementary approaches to optical quantum information processing have been pursued: qubits and continuous-variables, each exploiting either particle or wave nature of light.Both approaches have advantages and disadvantages in terms of the practical realization of optical quantum information processing (QIP).

Qubit QIP enables high fidelity of operations, but experimental realizations have been probabilistic and mostly required post-selection of successful events. This is due to the low creation and detection efficiencies of photonic qubits.
On the other hand, CV QIP is deterministic, thanks to on-demand entanglement resources and efficient homodyne measurement; however, the fidelity of operations is limited by the imperfection of the entanglement.
In recent years, there has been significant progress in combining both technologies with a view to realizing hybrid protocols that overcome the current limit ations of optical QIP.

This hybrid approach is analogous to the digital and analog hybrid signal processing in classical information processing: we set thresholds to digitize the originally continuous voltage signals.
In optical QIP, this threshold was given by nature as the wave-particle duality of light.Therefore it naturally follows to take advantage of both features in optical QIP as well. 

Here we experimentally realize fully deterministic quantum teleportation of photonic qubits without post-selection. The key step is to make use of a hybrid technique involving continuous-variable teleportation of a discrete-variable, photonic qubit. This hybrid quantum teleporation opens way to many sophisticated protocols for quantum communication high fidelity, highly efficient and commutation.

Next we apply hybrid techniques to delve into the fundamentals of quantum mechanics.We demonstrate the nonlocal wavefunction collapse for a single particle, the idea of which dates back to Einstein’s first argument on his concerns about quantum theory, by performing EPR-steering using heralded single photons.Here we experimentally realize fully deterministic quantum teleportation of photonic qubits without post-selection. 

*References:

S. Takeda, T. Mizuta, M. Fuwa, P. van Loock and A. Furusawa "Deterministic quantum teleportation of photonic quantum bits by a hybrid technique"

Nature 500, 315-318 (2013).