Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Y23: Invited Session: Quantum Bath Engineering with Superconducting Circuits |
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Sponsoring Units: DCMP GQI Chair: Alexandre Blais, Universite de Sherbrooke Room: 505-507 |
Friday, March 7, 2014 8:00AM - 8:36AM |
Y23.00001: Taking Control of Superconducting Qubits Invited Speaker: Irfan Siddiqi One of the fundamental challenges in quantum information processing is to sustain coherence over a time interval practical for performing a computation or simulation. Until recently, boosting coherence has involved hardware development to minimize coupling to a dissipative environment which typically transforms a quantum superposition into a classical state. In the domain of superconducting circuits, the development of robust quantum-noise-limited microwave amplifiers and quantum bits with lifetimes in excess of 100 microseconds has enabled the use of bath engineering to actively suppress decoherence. In particular, we have been able to tailor the dissipative environment, either via measurement or control pulses, to stabilize quantum superposition states and coherent oscillations indefinitely, generate entanglement, and maintain a pure quantum state by real-time tracking. Future directions for improving measurement efficiency and architectures for on-chip measurement in a multi-qubit setting will also be discussed. [Preview Abstract] |
Friday, March 7, 2014 8:36AM - 9:12AM |
Y23.00002: Autonomously stabilized entanglement between two superconducting qubits Invited Speaker: Shyam Shankar Quantum error-correction codes are designed to protect an arbitrary state of a multi-qubit register against decoherence-induced errors, but their implementation is an outstanding challenge for the development of large-scale quantum computers. A first step is to stabilize a non-equilibrium state of a simple quantum system such as a qubit or a cavity mode, in the presence of decoherence. Several groups have recently accomplished this goal using measurement-based feedback schemes. A next step is to prepare and stabilize a state of a composite system. Here we demonstrate the stabilization of an entangled Bell state of a quantum register of two superconducting qubits for an arbitrary time. Our result [1] is achieved by an autonomous feedback scheme which combines continuous drives along with a specifically engineered coupling between the two-qubit register and a dissipative bath. Similar bath engineering techniques have recently been used for qubit reset, single qubit state stabilization, as well as for the creation and stabilization of states of multipartite quantum systems. Unlike conventional, measurement-based schemes, an autonomous approach which uses engineered dissipation to counteract decoherence, obviates the need for a complicated external feedback loop to correct errors. Instead the feedback loop is built into the Hamiltonian such that the steady state of the system in the presence of drives and dissipation is a Bell state, an essential building-block for quantum information processing. Such autonomous schemes, which are broadly applicable to a variety of physical systems, will be an essential tool for the implementation of quantum-error correction.\\[4pt] [1] \texttt{http://dx.doi.org/10.1038/nature12802} [Preview Abstract] |
Friday, March 7, 2014 9:12AM - 9:48AM |
Y23.00003: Dissipation engineering in a coherent feedback electromechanical network Invited Speaker: Joseph Kerckhoff Modern superconducting microwave circuit experiments often consist of a quantum circuit under study, followed by a quantum-limited microwave amplifier. The subfield of quantum electromechanics, in which the quantum circuit is a mechanical resonator coupled to a microwave resonator, is no exception. However, a simple modification of the cables between these devices turns this open-loop, serial network into a fully-cryogenic, coherent feedback network. In effect, this easy-to-build network becomes a brand new kind of device, with useful and novel dynamics. Applied to an electromechanical context, the microwave and electromechanical dissipation is greatly modified through these closed loop dynamics, leading to dynamically tunable and phase-sensitive decay. We experimentally demonstrate that the microwave decay rate may be modulated by at least a factor of 10 at a rate greater than $10^4$ times the mechanical response rate. Similarly, the mechanical state can be dynamically squeezed and unsqueezed. While we have only investigated dynamics in the classical regime, we expect analogous behavior in the quantum regime. Finally, this approach is suitable for both 3D and planar architectures. I will describe my observations of this network and the general utility of networks of modular quantum circuits to dissipation engineering. [Preview Abstract] |
Friday, March 7, 2014 9:48AM - 10:24AM |
Y23.00004: Perfect squeezing by damping modulation in circuit quantum electrodynamics Invited Speaker: Nicolas Didier Dissipation-driven quantum state engineering uses the environment to steer the state of quantum systems and preserve quantum coherence in the steady state. We theoretically show that modulating the damping rate of a microwave resonator generates a new squeezing mechanism that creates a vacuum squeezed state of arbitrary squeezing strength, thereby allowing perfect squeezing. Given the recent experimental realizations in circuit QED of a microwave resonator with a tunable damping rate, superconducting circuits are an ideal playground to implement this technique. By dispersively coupling a qubit to the microwave resonator, it is possible to obtain qubit-state dependent squeezing. Moreover, when two qubits are coupled to the resonator, damping modulation can be used to produce entanglement between the qubits. Preprint: arXiv:1307.5311. [Preview Abstract] |
Friday, March 7, 2014 10:24AM - 11:00AM |
Y23.00005: Optomechanical entanglement via reservoir engineering Invited Speaker: Yingdan Wang A mechanical resonator could serve as an ideal system for transferring quantum states and mediating interactions between very different kinds of photons. To this end, recent experiments have realized three-mode optomechanical systems, where a single mechanical resonator simultaneously interacts with both an optical and a microwave cavity. In this talk I will discuss different strategies which use reservoir engineering in such a system as a powerful tool to generate robust, stationary entanglement between the two cavity fields. By manipulating the mechanical resonator to effectively cool delocalized Bogoliubov modes, we find that large intracavity entanglement can be achieved [1], at a level which is well above the maximum achievable via a coherent two-mode interaction. We have also analyzed the entanglement of the output fields of the two cavities. While there are significant differences from the intra-cavity fields, we again find that with proper parameter choices, large amounts of entanglement can be achieved. While the emphasis is on optomechanics, our results can also be applied directly to other 3-mode bosonic systems (e.g., as could be realized with superconducting microwave circuits). \\[4pt] [1] Ying-Dan Wang and A. A. Clerk, Phys. Rev. Lett. 110, 253601 (2013). [Preview Abstract] |
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