48 research outputs found
Superconducting Quantum Metamaterials
Superconducting quantum metamaterials extend the idea of their classical counterpart to a regime where their constituent meta-atoms are quantum objects, which can hold their quantum coherence for longer than the propagation time of light through the medium.
In this work, we have realized a quantum metamaterial consisting of eight individually controllable superconducting transmon qubits, which are coupled to the mode continuum of a one-dimensional coplanar waveguide. This system can be described within the framework of waveguide-quantum electrodynamics, which predicates that the mutual interaction of the qubits with the waveguide gives rise to long-range interactions of the qubits.
In spectroscopic measurements we observe the formation of super- and subradiant collective metamaterial excitations, as well as the emergence of a polaritonic band gap and study their dependence on the number of participating resonant qubits. We utilize the collective Autler-Townes splitting of the metamaterial to demonstrate control over its band gap. Furthermore, we exploit the control over the band structure for a first realization of slowly propagating light in the metamaterial. Our findings show that superconducting quantum metamaterials are a suitable platform to study fundamental excitations in solids and pave way to applications in quantum information processing like quantum memories
Quantum sensors for microscopic tunneling systems
The anomalous low-temperature properties of glasses arise from intrinsic
excitable entities, so-called tunneling Two-Level-Systems (TLS), whose
microscopic nature has been baffling solid-state physicists for decades. TLS
have become particularly important for micro-fabricated quantum devices such as
superconducting qubits, where they are a major source of decoherence. Here, we
present a method to characterize individual TLS in virtually arbitrary
materials deposited as thin-films. The material is used as the dielectric in a
capacitor that shunts the Josephson junction of a superconducting qubit. In
such a hybrid quantum system the qubit serves as an interface to detect and
control individual TLS. We demonstrate spectroscopic measurements of TLS
resonances, evaluate their coupling to applied strain and DC-electric fields,
and find evidence of strong interaction between coherent TLS in the sample
material. Our approach opens avenues for quantum material spectroscopy to
investigate the structure of tunneling defects and to develop low-loss
dielectrics that are urgently required for the advancement of superconducting
quantum computers
Probing the Tavis-Cummings level splitting with intermediate-scale superconducting circuits
We demonstrate the local control of up to eight two-level systems interacting
strongly with a microwave cavity. Following calibration, the frequency of each
individual two-level system (qubit) is tunable without influencing the others.
Bringing the qubits one by one on resonance with the cavity, we observe the
collective coupling strength of the qubit ensemble. The splitting scales up
with the square root of the number of the qubits, which is the hallmark of the
Tavis-Cummings model. The local control circuitry causes a bypass shunting the
resonator, and a Fano interference in the microwave readout, whose contribution
can be calibrated away to recover the pure cavity spectrum. The simulator's
attainable size of dressed states with up to five qubits is limited by reduced
signal visibility, and -- if uncalibrated -- by off-resonance shifts of
sub-components. Our work demonstrates control and readout of quantum coherent
mesoscopic multi-qubit system of intermediate scale under conditions of noise
Waveguide Bandgap Engineering with an Array of Superconducting Qubits
Waveguide quantum electrodynamics offers a wide range of possibilities to
effectively engineer interactions between artificial atoms via a
one-dimensional open waveguide. While these interactions have been
experimentally studied in the few qubit limit, the collective properties of
such systems for larger arrays of qubits in a metamaterial configuration has so
far not been addressed. Here, we experimentally study a metamaterial made of
eight superconducting transmon qubits with local frequency control coupled to
the mode continuum of a waveguide. By consecutively tuning the qubits to a
common resonance frequency we observe the formation of super- and subradiant
states, as well as the emergence of a polaritonic bandgap. Making use of the
qubits quantum nonlinearity, we demonstrate control over the latter by inducing
a transparency window in the bandgap region of the ensemble. The circuit of
this work extends experiments with one and two qubits towards a full-blown
quantum metamaterial, thus paving the way for large-scale applications in
superconducting waveguide quantum electrodynamics.Comment: 7 pages, 4 figure
Waveguide bandgap engineering with an array of superconducting qubits
Waveguide quantum electrodynamics offers a wide range of possibilities to effectively engineer interactions between artificial atoms via a one-dimensional open waveguide. While these interactions have been experimentally studied in the few qubit limit, the collective properties of such systems for larger arrays of qubits in a metamaterial configuration has so far not been addressed. Here, we experimentally study a metamaterial made of eight superconducting transmon qubits with local frequency control coupled to the mode continuum of a waveguide. By consecutively tuning the qubits to a common resonance frequency we observe the formation of super- and subradiant states, as well as the emergence of a polaritonic bandgap. Making use of the qubits quantum nonlinearity, we demonstrate control over the latter by inducing a transparency window in the bandgap region of the ensemble. The circuit of this work extends experiments with one and two qubits toward a full-blown quantum metamaterial, thus paving the way for large-scale applications in superconducting waveguide quantum electrodynamics
Quantum emulation of the transient dynamics in the multistate Landau-Zener model
Quantum simulation is one of the most promising near term applications of quantum computing. Especially, systems with a large Hilbert space are hard to solve for classical computers and thus ideal targets for a simulation with quantum hardware. In this work, we study experimentally the transient dynamics in the multistate Landau-Zener model as a function of the Landau-Zener velocity. The underlying Hamiltonian is emulated by superconducting quantum circuit, where a tunable transmon qubit is coupled to a bosonic mode ensemble comprising four lumped element microwave resonators. We investigate the model for different initial states: Due to our circuit design, we are not limited to merely exciting the qubit, but can also pump the harmonic modes via a dedicated drive line. Here, the nature of the transient dynamics depends on the average photon number in the excited resonator. The greater effective coupling strength between qubit and higher Fock states results in a quasi-adiabatic transition, where coherent quantum oscillations are suppressed without the introduction of additional loss channels. Our experiments pave the way for more complex simulations with qubits coupled to an engineered bosonic mode spectrum
Slowing down light in a qubit metamaterial
The rapid progress in quantum information processing leads to a rising demand for devices to control the propagation of electromagnetic wave pulses and to ultimately realize universal and efficient quantum memory. While in recent years, significant progress has been made to realize slow light and quantum memories with atoms at optical frequencies, superconducting circuits in the microwave domain still lack such devices. Here, we demonstrate slowing down electromagnetic waves in a superconducting metamaterial composed of eight qubits coupled to a common waveguide, forming a waveguide quantum electrodynamics system. We analyze two complementary approaches, one relying on dressed states of the Autler–Townes splitting and the other based on a tailored dispersion profile using the qubits tunability. Our time-resolved experiments show reduced group velocities of down to a factor of about 1500 smaller than in vacuum. Depending on the method used, the speed of light can be controlled with an additional microwave tone or an effective qubit detuning. Our findings demonstrate high flexibility of superconducting circuits to realize custom band structures and open the door to microwave dispersion engineering in the quantum regime
Slowing down light in a qubit metamaterial
The rapid progress in quantum information processing leads to a rising demand for devices to control the propagation of electromagnetic wave pulses and to ultimately realize universal and efficient quantum memory. While in recent years, significant progress has been made to realize slow light and quantum memories with atoms at optical frequencies, superconducting circuits in the microwave domain still lack such devices. Here, we demonstrate slowing down electromagnetic waves in a superconducting metamaterial composed of eight qubits coupled to a common waveguide, forming a waveguide quantum electrodynamics system. We analyze two complementary approaches, one relying on dressed states of the Autler–Townes splitting and the other based on a tailored dispersion profile using the qubits tunability. Our time-resolved experiments show reduced group velocities of down to a factor of about 1500 smaller than in vacuum. Depending on the method used, the speed of light can be controlled with an additional microwave tone or an effective qubit detuning. Our findings demonstrate high flexibility of superconducting circuits to realize custom band structures and open the door to microwave dispersion engineering in the quantum regime
Coherent superconducting qubits from a subtractive junction fabrication process
Josephson tunnel junctions are the centerpiece of almost any superconducting
electronic circuit, including qubits. Typically, the junctions for qubits are
fabricated using shadow evaporation techniques to reduce dielectric loss
contributions from the superconducting film interfaces. In recent years,
however, sub-micron scale overlap junctions have started to attract attention.
Compared to shadow mask techniques, neither an angle dependent deposition nor
free-standing bridges or overlaps are needed, which are significant limitations
for wafer-scale processing. This comes at the cost of breaking the vacuum
during fabrication, but simplifies integration in multi-layered circuits,
implementation of vastly different junction sizes, and enables fabrication on a
larger scale in an industrially-standardized process. In this work, we
demonstrate the feasibility of a subtractive process for fabrication of overlap
junctions. In an array of test contacts, we find low aging of the average
normal state resistance of only 1.6\% over 6 months. We evaluate the coherence
properties of the junctions by employing them in superconducting transmon
qubits. In time domain experiments, we find that both, the qubit life- and
coherence time of our best device, are on average greater than
20\,\si{\micro\second}. Finally, we discuss potential improvements to our
technique. This work paves the way towards a more standardized process flow
with advanced materials and growth processes, and constitutes an important step
for large scale fabrication of superconducting quantum circuits.Comment: 8 pages, 7 figure