29 research outputs found
Quantum simulation experiments with superconducting circuits
While the universal quantum computer seems not in reach for the near future, this work focusses on analog quantum simulation of intriguing quantum models of light-matter interactions, with the goal of achieving a computational speed-up as compared to classical hardware. Existing building blocks of quantum hardware are used from superconducting circuits, that have proven to be a very suitable experimental platform for the implementation of model Hamiltonians at a high degree of controllability
Emulating the one-dimensional Fermi-Hubbard model by a double chain of qubits
The Jordan-Wigner transformation maps a one-dimensional (1D) spin-
1
/
2
system onto a fermionic model without spin degree of freedom. A double chain of quantum bits with
X
X
and
Z
Z
couplings of neighboring qubits along and between the chains, respectively, can be mapped on a spin-full 1D Fermi-Hubbard model. The qubit system can thus be used to emulate the quantum properties of this model. We analyze physical implementations of such analog quantum simulators, including one based on transmon qubits, where the
Z
Z
interaction arises due to an inductive coupling and the
X
X
interaction due to a capacitive interaction. We propose protocols to gain confidence in the results of the simulation through measurements of local operators
Analog quantum simulation of the Rabi model in the ultra-strong coupling regime
The quantum Rabi model describes the fundamental mechanism of light-matter
interaction. It consists of a two-level atom or qubit coupled to a quantized
harmonic mode via a transversal interaction. In the weak coupling regime, it
reduces to the well-known Jaynes-Cummings model by applying a rotating wave
approximation (RWA). The RWA breaks down in the ultra-strong coupling (USC)
regime, where the effective coupling strength is comparable to the energy
of the bosonic mode, and remarkable features in the system dynamics
are revealed. We demonstrate an analog quantum simulation of an effective
quantum Rabi model in the USC regime, achieving a relative coupling ratio of
. The quantum hardware of the simulator is a superconducting
circuit embedded in a cQED setup. We observe fast and periodic quantum state
collapses and revivals of the initial qubit state, being the most distinct
signature of the synthesized model.Comment: 20 pages, 13 figure
Realizing the two-dimensional hard-core Bose-Hubbard model with superconducting qubits
The pursuit of superconducting-based quantum computers has advanced the
fabrication of and experimentation with custom lattices of qubits and
resonators. Here, we describe a roadmap to use present experimental
capabilities to simulate an interacting many-body system of bosons and measure
quantities that are exponentially difficult to calculate numerically. We focus
on the two-dimensional hard-core Bose-Hubbard model implemented as an array of
floating transmon qubits. We describe a control scheme for such a lattice that
can perform individual qubit readout and show how the scheme enables the
preparation of a highly-excited many-body state, in contrast with atomic
implementations restricted to the ground state or thermal equilibrium. We
discuss what observables could be accessed and how they could be used to better
understand the properties of many-body systems, including the observation of
the transition of eigenstate entanglement entropy scaling from area law
behavior to volume law behaviorComment: 14 pages, 8 figure
Quantum simulation of the spin-boson model with a microwave circuit
We consider superconducting circuits for the purpose of simulating the
spin-boson model. The spin-boson model consists of a single two-level system
coupled to bosonic modes. In most cases, the model is considered in a limit
where the bosonic modes are sufficiently dense to form a continuous spectral
bath. A very well known case is the ohmic bath, where the density of states
grows linearly with the frequency. In the limit of weak coupling or large
temperature, this problem can be solved numerically. If the coupling is strong,
the bosonic modes can become sufficiently excited to make a classical
simulation impossible. Here, we discuss how a quantum simulation of this
problem can be performed by coupling a superconducting qubit to a set of
microwave resonators. We demonstrate a possible implementation of a continuous
spectral bath with individual bath resonators coupling strongly to the qubit.
Applying a microwave drive scheme potentially allows us to access the
strong-coupling regime of the spin-boson model. We discuss how the resulting
spin relaxation dynamics with different initialization conditions can be probed
by standard qubit-readout techniques from circuit quantum electrodynamics.Comment: 23 pages, 10 figure
Local Sensing with the Multi-Level AC Stark Effect
Analyzing weak microwave signals in the GHz regime is a challenging task if
the signal level is very low and the photon energy widely undefined. A
superconducting qubit can detect signals in the low photon regime, but due to
its discrete level structure, it is only sensitive to photons of certain
energies. With a multi-level quantum system (qudit) in contrast, the unknown
signal frequency and amplitude can be deduced from the higher level AC Stark
shift. The measurement accuracy is given by the signal amplitude, its detuning
from the discrete qudit energy level structure and the anharmonicity. We
demonstrate an energy sensitivity in the order of with a measurement
range of more than . Here, using a transmon qubit, we
experimentally observe shifts in the transition frequencies involving up to
three excited levels. These shifts are in good agreement with an analytic
circuit model and master equation simulations. For large detunings, we find the
shifts to scale linearly with the power of the applied microwave drive.
Exploiting the effect, we demonstrated a power meter which makes it possible to
characterize the microwave transmission from source to sample.Comment: 10 pages, 7 figure
Microwave Packaging for Superconducting Qubits
Over the past two decades, the performance of superconducting quantum
circuits has tremendously improved. The progress of superconducting qubits
enabled a new industry branch to emerge from global technology enterprises to
quantum computing startups. Here, an overview of superconducting quantum
circuit microwave control is presented. Furthermore, we discuss one of the
persistent engineering challenges in the field, how to control the
electromagnetic environment of increasingly complex superconducting circuits
such that they are simultaneously protected and efficiently controllable
Multi-photon dressing of an anharmonic superconducting many-level quantum circuit
We report on the investigation of a superconducting anharmonic multi-level
circuit that is coupled to a harmonic readout resonator. We observe
multi-photon transitions via virtual energy levels of our system up to the
fifth excited state. The back-action of these higher-order excitations on our
readout device is analyzed quantitatively and demonstrated to be in accordance
with theoretical expectation. By applying a strong microwave drive we achieve
multi-photon dressing within our anharmonic circuit which is dynamically
coupled by a weak probe tone. The emerging higher-order Rabi sidebands and
associated Autler-Townes splittings involving up to five levels of the
investigated anharmonic circuit are observed. Experimental results are in good
agreement with master equation simulations.Comment: 9 pages, 5 figure