April 2015
Abstracts of the QSIT Lunch Seminar, Thursday, April 2, 2015
Heralded Phonon Entanglement on a Photonic Crystal Architecture
Hugo Flayac, EPF Lausanne
Cavity optomechanics [1] has demonstrated a spectacular theoretical and experimental development in the past decade and is now envisioned as one of the most promising route to produce nonclassical states of macroscopic degrees of freedom mediated by an optical field. Such achievements would not only shine light on quantum decoherence at a fundamental level but could provide a long living information storage platform for potential quantum repeaters.
The recent prowess in the optimization of Si or InP-based photonic crystal structures [2,3] allow now to combine outstanding quality factors of the cavity modes with localized vibration resulting in a sizeable optomechanical coupling. Such highly integrable and low footprint solid state structures lie among the best candidates for the future of quantum logic elements.
In that context, we propose a realistic heralding protocol for the preparation and readout of entangled phonons [4] within state of the art parameters measured in photonic crystal cavities and however easily extensible to other optomechanical systems. Our initial proposal relies on a cavity mode coupled to and a pair of mechanical modes and its sideband excitation. The mechanical entangled state is written through a Stokes process supplemented by a single photon detection and, readout through the anti-Stokes process producing a characteristic interference pattern at the cavity frequency.
Our procedure is not only extended to remote optomechanical systems but also to the formation of more complex entangled states of the W or NOON kind.
References:
[1] M. Aspelmeyer, T. J. Kippenberg, and F. Marquardt, arXiv:1303.0733 (2013).
[2] E. Gavartin et al., Phys. Rev. Lett. 106, 203902 (2011).
[3] J. Chan et al., Nature 478, 8992 (2011).
[4] H. Flayac and V. Savona, Phys. Rev. Lett. 113, 143603 (2014).
Digital quantum simulation of spin models with circuit quantum electrodynamics
Yves Salathé, Quantum Device Lab, ETH Zürich
Systems of interacting quantum spins show a rich spectrum of quantum phases and display interesting many-body dynamics. Computing characteristics of even small systems on conventional computers poses significant challenges. A quantum simulator has the potential to outperform standard computers in calculating the evolution of complex quantum systems. Here, we perform a digital quantum simulation of the paradigmatic Heisenberg and Ising interacting spin models using a two transmon-qubit circuit quantum electrodynamics setup. We make use of the exchange interaction naturally present in the simulator to construct a digital decomposition of the model specific evolution and extract its full dynamics. This approach is universal and efficient, employing only resources which are polynomial in the number of spins and indicates a path towards the controlled simulation of general spin dynamics in superconducting qubit platforms.
Reference to the paper: external pagehttp://arxiv.org/abs/1502.06778