Quantum Teleportation

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Quantum teleportation of an unknown input state from an outside source onto a quantum node is considered one of the key components of long-distance quantum communication protocols. It has already been demonstrated with pure photonic quantum systems as well as atomic and solid-state spin systems linked by photonic channels. Now, a team of researchers from the Netherlands, Brazil and China has demonstrated quantum teleportation of a polarization-encoded optical input state onto the joint state of a pair of nanomechanical resonators.
Schematic representation of the key steps of the teleportation protocol and its verification: (1) realization of an EPR source: the Stokes scattering of a pair of nanobeams results in an entangled state between the photon polarization state and the phonon population state in the nanobeams; (2) an arbitrary input state is encoded in the polarization basis of a weak coherent state; (3) a BSM of the polarization teleports the input state onto the joint mechanical memory state; (4) a short anti-Stokes pulse maps the teleported state (ψout) back onto the photon polarization for verification. Image credit: Fiaschi et al., doi: 10.1038/s41566-021-00866-z.
“The use of optomechanical devices is a breakthrough because they can be designed to operate at any optical wavelength, including the low-loss infrared telecom fiber wavelengths,” said Dr. Simon Gröblacher, a researcher in the Kavli Institute of Nanoscience and the Department of Quantum Nanoscience at Delft University of Technology.
“It is this wavelength that results in the lowest transmission loss, allowing the longest distance between repeater nodes.”
“This milestone was possible due to the quality and flexibility of our nanofabricated optomechanical systems, which, unlike most other quantum systems, allow for independently engineered optical properties. A future quantum internet will undoubtedly make use of the existing telecom network at this wavelength.”
In their experiments, Dr. Gröblacher and colleagues created a polarization-encoded photonic qubit in an arbitrary quantum state.
They then transported this photon over tens of meters of optical fiber and teleported it onto their quantum memory comprised of two massive, mechanical silicon resonators — each about 10 micrometers in size and consisting of tens of billions of atoms.
The quantum information was stored in the single-excitation subspace of the two resonators.
To test the reliability of the process, the researchers further demonstrated that they could faithfully retrieve this teleported state from the memory.
“We now have to further improve the performance to the level required for a system that can be deployed in a real-world application, such as increasing the repetition rates, fidelities and the success-rate of the qubit teleportation and storage,” Dr. Gröblacher said.
“One route will be to design optomechanical systems that are resilient to parasitic optical absorption,” said Dr. Thiago Alegre, a researcher at the University of Campinas.
“This can be realized due to the flexibility of these nanofabricated devices.”
This research is a big step towards the team’s vision of a future hybrid quantum internet.
“We are working towards a heterogeneous network where you have various physical systems communicating and performing different functionalities,” Dr. Gröblacher said.
“You may have optomechanical quantum repeater nodes connected to a quantum computer or memory consisting of superconducting qubits or spin quantum systems, respectively.”
“All of these will have to be compatible with one another and operate at the same wavelength in order to faithfully transfer quantum information.”
The study was published in the journal Nature Photonics.
N. Fiaschi et al. Optomechanical quantum teleportation. Nat. Photon, published online October 7, 2021; doi: 10.1038/s41566-021-00866-z


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