Christian Reichl

Single-Shot Correlations and Two-Qubit Gate of Solid-State Spins

Independent readout of two single-spin qubits in quantum dots is achieved in an all-electrical setup. Measurement of coupled quantum systems plays a central role in quantum information processing. We have realized independent single-shot read-out of two electron spins in a double quantum dot. The read-out method is all-electrical, cross-talk between the two measurements is negligible, and read-out fidelities are ~86% on average. This allows us to directly probe the anticorrelations between two spins prepared in a singlet state and to demonstrate the operation of the two-qubit exchange gate on a complete set of basis states. The results provide a possible route to the realization and efficient characterization of multiqubit quantum circuits based on single quantum dot spins.

Long-distance coherent coupling in a quantum dot array

Controlling long-distance quantum correlations is central to quantum computation and simulation. In quantum dot arrays, experiments so far rely on nearest-neighbour couplings only, and inducing long-distance correlations requires sequential local operations. Here, we show that two distant sites can be tunnel-coupled directly. The coupling is mediated by virtual occupation of an intermediate site, with a strength that is controlled via the energy detuning of this site. It permits a single charge to oscillate coherently between the outer sites of a triple dot array without passing through the middle, as demonstrated through the observation of Landau-Zener-Stückelberg interference. The long-distance coupling significantly improves the prospects of fault-tolerant quantum computation using quantum dot arrays, and opens up new avenues for performing quantum simulations in nanoscale devices.

Direct mapping of the formation of a persistent spin helix

Spin–orbit interaction induces spin-polarization decay in semiconductor quantum wells. But this decay can be suppressed in favour of a helical spin mode by tuning the interaction. Optical pump–probe measurements provide direct evidence of the resulting helix—a signature that has so far only been inferred from transport measurements.

Ultrastrong coupling in the near field of complementary split-ring resonators

Ultrastrong coupling of split ring resonators to the cyclotron transition in two-dimensional electron gases is studied in the terahertz regime, clarifying the importance of the resonator geometry. The use of the complementary type of resonator allows removal of the signal from the uncoupled areas. The experimental results are of spectacular quality and quantity. A record high light-matter coupling ratio (normalized vacuum Rabi frequency) of 0.87 is achieved.

Strong Coupling Cavity QED with Gate-Defined Double Quantum Dots Enabled by a High Impedance Resonator

The strong coupling limit of cavity quantum electrodynamics (QED) implies the capability of a matter-like quantum system to coherently transform an individual excitation into a single photon within a resonant structure. This not only enables essential processes required for quantum information processing but also allows for fundamental studies of matter-light interaction. In this work we demonstrate strong coupling between the charge degree of freedom in a gate-detuned GaAs double quantum dot (DQD) and a frequency-tunable high impedance resonator realized using an array of superconducting quantum interference devices (SQUIDs). In the resonant regime, we resolve the vacuum Rabi mode splitting of size

Microwave Emission from Hybridized States in a Semiconductor Charge Qubit

2g/2\pi = 238

Transport properties of clean quantum point contacts

MHz at a resonator linewidth

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

\kappa/2\pi = 12

Single-electron double quantum dot dipole-coupled to a single photonic mode

MHz and a DQD charge qubit dephasing rate of

Interference of electrons in backscattering through a quantum point contact

\gamma_2/2\pi = 80