Simone Gasparinetti

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

Rapid High-Fidelity Single-Shot Dispersive Readout of Superconducting Qubits

2g/2pi = 238

Observation of topological Uhlmann phases with superconducting qubits

MHz at a resonator linewidth

Probing quantum interference effects in the work distribution

kappa/2pi = 12

Studying light-harvesting models with superconducting circuits

MHz and a DQD charge qubit dephasing rate of

Superconducting Switch for Fast On-Chip Routing of Quantum Microwave Fields

gamma_2/2pi = 80

Deterministic quantum state transfer and remote entanglement using microwave photons

MHz extracted independently from microwave spectroscopy in the dispersive regime. Our measurements indicate a viable path towards using circuit based cavity QED for quantum information processing in semiconductor nano-structures.

Measurement of a vacuum-induced geometric phase.

The speed of quantum gates and measurements is a decisive factor for the overall fidelity of quantum protocols when performed on physical qubits with finite coherence time. Reducing the time required to distinguish qubit states with high fidelity is therefore a critical goal in quantum information science. The state-of-the-art readout of superconducting qubits is based on the dispersive interaction with a readout resonator. Here, we bring this technique to its current limit and demonstrate how the careful design of system parameters leads to fast and high-fidelity measurements without affecting qubit coherence. We achieve this result by increasing the dispersive interaction strength, by choosing an optimal linewidth of the readout resonator, by employing a Purcell filter, and by utilizing phase-sensitive parametric amplification. In our experiment, we measure 98.25% readout fidelity in only 48 ns, when minimizing read-out time, and 99.2% in 88 ns, when maximizing the fidelity, limited predominantly by the qubit lifetime of 7.6 us. The presented scheme is also expected to be suitable for integration into a multiplexed readout architecture.

Publisher Correction: Studying light-harvesting models with superconducting circuits

Topological insulators and superconductors at finite temperature can be characterized by the topological Uhlmann phase. However, a direct experimental measurement of this invariant has remained elusive in condensed matter systems. Here, we report a measurement of the topological Uhlmann phase for a topological insulator simulated by a system of entangled qubits in the IBM Quantum Experience platform. By making use of ancilla states, otherwise unobservable phases carrying topological information about the system become accessible, enabling the experimental determination of a complete phase diagram including environmental effects. We employ a state-independent measurement protocol which does not involve prior knowledge of the system state. The proposed measurement scheme is extensible to interacting particles and topological models with a large number of bands.Topological matter: quantum simulation of the Uhlmann phaseA system of entangled qubits is used to simulate a topological insulator, measuring for the first time the topological Uhlmann phase. Observing the Uhlmann phase, which is the generalization of the Berry phase in presence of an environment, requires high level of control over the environmental degrees of freedom, making it unachievable in condensed matter systems. An international team led by Miguel A. Martin-Delgado of the Universidad Computense of Madrid has now shown how to simulate the Uhlmann phase in a system of three entangled qubits. By treating one qubit as system, one as environment and one as probe, the researchers could control the system-environment coupling well enough to detect the temperature-induced topological transition by interferometric means, and compute the topological phase diagram for qubits in the presence of noise.

Energy Transfer in a System of Coupled Superconducting Qubits

What is the role of coherence in determining the distribution of work done on a quantum system? We approach this question from an operational perspective and consider a setup in which the internal energy of a closed system is recorded by a quantum detector before and after the system is acted upon by an external drive. We find that the resulting work distribution depends on the initial state of the detector as well as on the choice of the final measurement. We consider two complementary measurement schemes, both of which show clear signatures of quantum interference. We specifically discuss how to implement these schemes in the circuit QED architecture, using an artificial atom as the system and a quantized mode of the electromagnetic field as the detector. Different measurement schemes can be realized by preparing the field either in a superposition of Fock states or in a coherent state and exploiting state-of-the art techniques for the characterization of microwave radiation at the quantum level. More generally, the single bosonic mode we utilize is arguably the minimal quantum detector capable of capturing the complementary aspects of the work distribution discussed here.