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Highlights for SOLID


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.

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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.

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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.

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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.

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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.

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