The efficient implementation of many-body interactions in superconducting circuits allows for the realization of multipartite entanglement and topological codes, as well as the efficientsimulation of highly-correlated fermionic systems. We propose the engineering of fast multiqubit interactions with tunable transmon-resonator couplings. This dynamics is obtained by the modulation of magnetic fluxes threading SQUID loops embedded in the transmon devices. We consider the feasibility of the proposed implementation in a realistic scenario and discuss potential applications.
We propose the implementation of a digital quantum simulator for prototypical spin models in a circuit quantum electrodynamics architecture. We consider the feasibility of the quantumsimulation of Heisenberg and frustrated Ising models in transmon qubits coupled to coplanar waveguide microwave resonators. Furthermore, we analyze the time evolution of these models and compare the ideal spin dynamics with a realistic version of the proposed quantum simulator. Finally, we discuss the key steps for developing the toolbox of digital quantum simulators in superconducting circuits.
Coherent generation of single photons with waveforms of a given shape plays an important role in many protocols for quantum information exchange between distant quantum bits. Here wecreate shaped microwave photons in a superconducting system consisting of a transmon circuit coupled to a transmission line resonator. Using the third level of the transmon, we exploit a second-order transition induced by a modulated microwave drive to controllably transfer an excitation to the resonator from which it is emitted into a transmission line as a travelling photon. We demonstrate the single-photon nature of the emitted field and the ability to generate photons with a controlled amplitude and phase. In contrast to similar schemes, the presented one requires only a single control line, allowing for a simple implementation with fixed-frequency qubits.
We make use of a superconducting qubit to study the effects of noise on
adiabatic geometric phases. The state of the system, an effective spin one-half
particle, is adiabatically guidedalong a closed path in parameter space and
thereby acquires a geometric phase. By introducing artificial fluctuations in
the control parameters, we measure the geometric contribution to dephasing for
a variety of noise powers and evolution times. Our results clearly show that
only fluctuations which distort the path lead to geometric dephasing. In a
direct comparison with the dynamic phase, which is path-independent, we observe
that the adiabatic geometric phase is less affected by noise-induced dephasing.
This observation directly points towards the potential of geometric phases for
quantum gates or metrological applications.
A localized qubit entangled with a propagating quantum field is well suited
to study non-local aspects of quantum mechanics and may also provide a channel
to communicate between spatiallyseparated nodes in a quantum network. Here, we
report the on demand generation and characterization of Bell-type entangled
states between a superconducting qubit and propagating microwave fields
composed of zero, one and two-photon Fock states. Using low noise linear
amplification and efficient data acquisition we extract all relevant
correlations between the qubit and the photon states and demonstrate
entanglement with high fidelity.
Geometric phases, which accompany the evolution of a quantum system and
depend only on its trajectory in state space, are commonly studied in two-level
systems. Here, however, we studythe adiabatic geometric phase in a weakly
anharmonic and strongly driven multi-level system, realised as a
superconducting transmon-type circuit. We measure the contribution of the
second excited state to the two-level geometric phase and find good agreement
with theory treating higher energy levels perturbatively. By changing the
evolution time, we confirm the independence of the geometric phase of time and
explore the validity of the adiabatic approximation at the transition to the
non-adiabatic regime.