Highlights for SOLID

Results tagged as highlights of the project.

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Mar 20, 2012

Quantum simulation of the ultrastrong coupling dynamics in circuit QED

We propose a method to get experimental access to the physics of the ultrastrong (USC) and deep strong (DSC) coupling regimes of light-matter interaction through the quantum simulation of their dynamics in standard circuit QED. The method makes use of a two-tone driving scheme, using state-of-the-art circuit-QED technology, and can be easily extended to general quantum optical cavity-QED setups. We provide examples of USC/DSC quantum effects that would be otherwise unaccessible.

Mar 20, 2012

Ultrafast Quantum Gates in Circuit QED

Ultrafast quantum gates in circuit QED: we have proposed the design of ultrafast gates in circuit QED by means of the access and suitable manipulation of the ultrastrong coupling regime in the qubit-cavity system.

G. Romero, D. Ballester, Y. M. Wang, V. Scarani, and E. Solano

Mar 6, 2012

Towards single electron spin resonance in a charge tunable quantum dot

Optical detected electron spin resonance is a powerful tool to study the coherence properties of electron spin coherence properties. In particular for an electron trapped in a single self-assembled quantum dot (QD) the electron spin coherence is strongly influenced by the nuclear spin dynamics; The electron interacts via hyperfine interaction with ~300000 nuclear spins whose random fluctuating distripution usually lead to significant reduction of electron spin coherence.

Mar 29, 2011

An electrically controllable spin qubit in a semiconductor nanowire

SOLID members from the Kavli Institute at TU-Delft have shown how spin-orbit interaction provides a way to control spins electrically. A spin–orbit quantum bit (qubit) is electrostatically defined in an indium arsenide nanowire, where the spin–orbit interaction is so strong that spin and motion can no longer be separated. In this regime, the group has realized fast qubit rotations and universal single-qubit control using only electric fields; the qubits are hosted in single-electron quantum dots that are individually addressable.

Mar 28, 2011

Strong Coupling of a Spin Ensemble to a Superconducting Resonator

Amongst all the microscopic quantum spin systems that can be coupled to superconducting circuits, negatively charged nitrogen- vacancy centers (N-V) in diamond are particularly attractive. One of the major reasons is that the spin coherence time has been shown to be as long as 2ms at room temperature. Compared to atoms, N-V centers are perfectly compatible with superconducting circuits, because they do not require challenging trapping techniques or large magnetic fields to bring them in resonance at GHz frequency with the circuit.

Mar 28, 2011

Probing the Temperature Dependence of an Individual Two-Level System via Coherent Control

The Karlsruhe groups of A. Ustinov and A. Shnirman (KTA) have demonstrated a new method to directly manipulate the state of individual two-level systems (TLSs) in phase qubits. The method allows one to characterize the coherence properties of TLSs using standard microwave pulse sequences, while the qubit is used only for state readout. The group has applied this method to perform the first measurement of the temperature dependence of TLS coherence.

Mar 28, 2011

Observation of the Bloch-Siegert Shift in a Qubit-Oscillator System in the Ultrastrong Coupling Regime

Here, the Mooij group at TU-Delft in close collaboration with group of SOLID theorist, E. Solano have measured the dispersive energy-level shift of an LC resonator magnetically coupled to a super- conducting qubit. The results clearly show that the system operates in the ultrastrong coupling regime of the light matter interaction. The large mutual kinetic inductance provides a coupling energy of ≈0.82GHz, requiring the addition of counter-rotating-wave terms in the description of the Jaynes-Cummings model.

Mar 28, 2011

Universal Dynamical Decoupling of a Single Solid-State Spin from a Spin Bath

Controlling the interaction of a single quantum system with its environment is a fundamental challenge in quantum science and technology. In this publication, the group of Ronald Hanson at TU-Delft managed to strongly suppress the coupling of a single spin in diamond with the surrounding spin bath by using double-axis dynamical decoupling. The coherence was preserved for arbitrary quantum states, as verified by quantum process tomography. The resulting coherence time enhancement followed a general scaling with the number of decoupling pulses.

Mar 28, 2011

Circuit quantum electrodynamics in the ultrastrong-coupling regime

In circuit quantum electrodynamics (QED), where superconducting artificial atoms are coupled to on-chip cavities, the strong-coupling regime has greatly evolved. In this regime, an atom and a cavity can exchange a photon frequently before coherence is lost. Nevertheless, all experiments so far are well described by the renowned Jaynes–Cummings model. In this work, the group at the Walter Meissner Institut in Garching, Germany collaborated closely with the SOLID theorist E.

Mar 28, 2011

Quantum-Dot-Spin Single-Photon Interface

In this paper SOLID researcher A. Imamoglu and colleagues at ETH-Zürich show how the spin-state-dependent resonance fluorescence from a charged quantum dot can be used to realize a classical single spin-photon interface. The measurement is background free and shows how detecting the scattered photon intensity with 300 ps time resolution projects the quantum dot spin into a definite spin eigenstate with a fidelity exceeding 99%. The bunching of resonantly scattered photons reveals information about electron spin dynamics.

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