Publications

Fragile topology in line-graph lattices with two, three, or four gapped flat bands

Citation:

C. S. Chiu, D. - S. Ma, Z. - D. Song, B. A. Bernevig, and A. A. Houck, “Fragile topology in line-graph lattices with two, three, or four gapped flat bands,” Physical Review Research, vol. 2, pp. 043414, 2020.
Fragile topology in line-graph lattices with two, three, or four gapped flat bands

Abstract:

The geometric properties of a lattice can have profound consequences on its band spectrum. For example, symmetry constraints and geometric frustration can give rise to topologicially nontrivial and dispersionless bands, respectively. Line-graph lattices are a perfect example of both of these features: Their lowest energy bands are perfectly flat, and here we develop a formalism to connect some of their geometric properties with the presence or absence of fragile topology in their flat bands. This theoretical work will enable experimental studies of fragile topology in several types of line-graph lattices, most naturally suited to superconducting circuits.

Publisher's Version

DOI:

10.1103/PhysRevResearch.2.043414

Floquet-Engineered Enhancement of Coherence Times in a Driven Fluxonium Qubit

Citation:

P. S. Mundada, A. Gyenis, Z. Huang, J. Koch, and A. A. Houck, “Floquet-Engineered Enhancement of Coherence Times in a Driven Fluxonium Qubit,” 2020.
Floquet-Engineered Enhancement of Coherence Times in a Driven Fluxonium Qubit

Abstract:

We use the quasienergy structure emerging in a periodically driven fluxonium superconducting circuit to encode quantum information with dynamically induced flux-insensitive sweet spots. The framework of Floquet theory provides an intuitive description of these high-coherence working points located away from the half-flux symmetry point of the undriven qubit. This approach offers flexibility in choosing the flux bias point and the energy of the logical qubit states as shown in Huang et al.[arXiv:2004.12458 (2020)]. We characterize the response of the system to noise in the modulation amplitude and dc flux bias, and experimentally demonstrate an optimal working point that is simultaneously insensitive against fluctuations in both. We observe a 40-fold enhancement of the qubit coherence times measured with Ramsey-type interferometry at the dynamical sweet spot compared with static operation at the same bias point.

Publisher's Version

Last updated on 11/17/2020

Engineering Dynamical Sweet Spots to Protect Qubits from 1/f Noise

Citation:

Z. Huang, P. S. Mundada, A. Gyenis, D. I. Schuster, A. A. Houck, and J. Koch, “Engineering Dynamical Sweet Spots to Protect Qubits from 1/f Noise,” arXiv: 2004.12458, 2020.
Engineering Dynamical Sweet Spots to Protect Qubits from 1/f Noise

Abstract:

Protecting superconducting qubits from low-frequency noise is essential for advancing superconducting quan- tum computation. We here introduce a protocol for engineering dynamical sweet spots which reduce the sus- ceptibility of a qubit to low-frequency noise. Based on the application of periodic drives, the location of the dynamical sweet spots can be obtained analytically in the framework of Floquet theory. In particular, for the example of fluxonium biased slightly away from half a flux quantum, we predict an enhancement of pure- dephasing by three orders of magnitude. Employing the Floquet eigenstates as the computational basis, we show that high-fidelity single-qubit gates can be implemented while maintaining dynamical sweet-spot opera- tion. We further confirm that qubit readout can be performed by adiabatically mapping the Floquet states back to the static qubit states, and subsequently applying standard measurement techniques. Our work provides an in- tuitive tool to encode quantum information in robust, time-dependent states, and may be extended to alternative architectures for quantum information processing.

Last updated on 07/21/2020

Quantum control of an oscillator using a stimulated Josephson nonlinearity

Citation:

A. Vrajitoarea, Z. Huang, P. Groszkowsi, J. Koch, and A. A. Houck, “Quantum control of an oscillator using a stimulated Josephson nonlinearity,” Nature Physics, vol. 16, pp. 211-217, 2020.
Quantum control of an oscillator using a stimulated Josephson nonlinearity

Publisher's Version

DOI:

10.1038/s41567-019-0703-5

Full Text

Superconducting circuits extensively rely on the Josephson junction as a nonlinear electronic element for manipulating quantum information and mediating photon interactions. Despite continuing efforts in pushing the coherence of Josephson circuits, the best photon lifetimes have been demonstrated in microwave cavities. Nevertheless, architectures based on quantum memories require a qubit element for logical operations at the cost of introducing additional loss channels and limiting process fidelities. Here, we directly operate the oscillator as an isolated two-level system by tailoring its Hilbert space. Implementing a flux-tunable inductive coupling between two resonators, we can selectively Rabi drive the lowest eigenstates by dynamically activating a three-wave interaction through parametric flux modulation. Measuring the Wigner function confirms that we can prepare arbitrary states confined in the single-photon manifold, with measured coherence times limited by the oscillator intrinsic quality factor. This architectural shift in engineering oscillators with stimulated nonlinearity can be exploited for designing long-lived quantum modules and offers flexibility in studying non-equilibrium physics with photons in a field-programmable simulator.
Last updated on 07/21/2020

Line-Graph Lattices: Euclidean and Non-Euclidean Flat Bands, and Implementations in Circuit Quantum Electrodynamics

Citation:

A. J. Kollár, M. Fitzpatrick, P. Sarnak, and A. A. Houck, “Line-Graph Lattices: Euclidean and Non-Euclidean Flat Bands, and Implementations in Circuit Quantum Electrodynamics,” Communications in Mathematical Physics, vol. 376, pp. 1909-1956, 2019.
Line-Graph Lattices: Euclidean and Non-Euclidean Flat Bands, and Implementations in Circuit Quantum Electrodynamics

Notes:

Materials science and the study of the electronic properties of solids are a major field of interest in both physics and engineering. The starting point for all such calculations is single-electron, or non-interacting, band structure calculations, and in the limit of strong on-site confinement this can be reduced to graph-like tight-binding models. In this context, both mathematicians and physicists have developed largely independent methods for solving these models. In this paper we will combine and present results from both fields. In particular, we will discuss a class of lattices which can be realized as line graphs of other lattices, both in Euclidean and hyperbolic space. These lattices display highly unusual features including flat bands and localized eigenstates of compact support. We will use the methods of both fields to show how these properties arise and systems for classifying the phenomenology of these lattices, as well as criteria for maximizing the gaps. Furthermore, we will present a particular hardware implementation using superconducting coplanar waveguide resonators that can realize a wide variety of these lattices in both non-interacting and interacting form

Publisher's Version

DOI:

10.1007/s00220-019-03645-8
Last updated on 07/21/2020

A low-disorder metal-oxide-silicon double quantum dot

Citation:

J. S. Kim, T. M. Hazard, A. A. Houck, and S. A. Lyon, “A low-disorder metal-oxide-silicon double quantum dot,” Applied Physics Letters, vol. 114, pp. 043501, 2019.
A low-disorder metal-oxide-silicon double quantum dot

ISSN:

00036951

Abstract:

One of the biggest challenges impeding the progress of Metal-Oxide-Silicon (MOS) quantum dot devices is the presence of disorder at the Si/SiO\$\_2\$ interface which interferes with controllably confining single and few electrons. In this work we have engineered a low-disorder MOS quantum double-dot device with critical electron densities, i.e. the lowest electron density required to support a conducting pathway, approaching critical electron densities reported in high quality Si/SiGe devices and commensurate with the lowest critical densities reported in any MOS device. Utilizing a nearby charge sensor, we show that the device can be tuned to the single-electron regime where charging energies of \$\backslashapprox\$8 meV are measured in both dots, consistent with the lithographic size of the dot. Probing a wide voltage range with our quantum dots and charge sensor, we detect three distinct electron traps, corresponding to a defect density consistent with the ensemble measured critical density. Low frequency charge noise measurements at 300 mK indicate a 1/\$f\$ noise spectrum of 3.4 \$\backslashmu\$eV/Hz\$\^\1/2\\$ at 1 Hz and magnetospectroscopy measurements yield a valley splitting of 110\$\backslashpm\$26 \$\backslashmu\$eV. This work demonstrates that reproducible MOS spin qubits are feasible and represents a platform for scaling to larger qubit systems in MOS.

Notes:

One of the biggest challenges impeding the progress of metal-oxide-silicon (MOS) quantum dot devices is the presence of disorder at the Si/SiO2 interface which interferes with controllably confining single and few electrons. In this work, we have engineered a low-disorder MOS quantum double-dot device with critical electron densities, i.e., the lowest electron density required to support a conducting pathway, approaching critical electron densities reported in high quality Si/SiGe devices and commensurate with the lowest critical densities reported in any MOS device. Utilizing a nearby charge sensor, we show that the device can be tuned to the single-electron regime where charging energies of 􏰃8 meV are measured in both dots, consistent with the lithographic size of the dot. Probing a wide voltage range with our quantum dots and charge sensor, we detect three dis- tinct electron traps, corresponding to a defect density consistent with the ensemble measured critical density. Low frequency charge noise measurements at 300 mK indicate a 1/f noise spectrum of 3.4 leV/Hz1=2 at 1 Hz and magnetospectroscopy measure- ments yield a valley splitting of 110 6 26 leV. This work demonstrates that reproducible MOS spin qubits are feasible and repre- sent a platform for scaling to larger qubit systems in MOS.

Publisher's Version

DOI:

10.1063/1.5075486
Last updated on 07/21/2020

Suppression of Qubit Crosstalk in a Tunable Coupling Superconducting Circuit

Citation:

P. S. Mundada, G. Zhang, T. Hazard, and A. A. Houck, “Suppression of Qubit Crosstalk in a Tunable Coupling Superconducting Circuit,” Physics Review Applied, vol. 12, pp. 054023, 2018.
Suppression of Qubit Crosstalk in a Tunable Coupling Superconducting Circuit

Abstract:

We report the suppression of static ZZ crosstalk in a two-qubit, two-coupler superconducting circuit, where the ZZ interaction between the two qubits can be tuned to near zero. Characterization of qubit crosstalk is performed using randomized benchmarking and a two-qubit iSWAP gate is implemented using parametric modulation. We observe the dependence of single-qubit gate fidelity on ZZ interaction strength and identify effective thermalization of the tunable coupler as a crucial prerequisite for high fidelity two-qubit gates.

Notes:

Parasitic crosstalk in superconducting quantum devices is a leading limitation for quantum gates. We demonstrate the suppression of static ZZ crosstalk in a two-qubit, two-coupler superconducting circuit, where the frequency of a tunable coupler can be adjusted such that the ZZ interaction from each coupler destructively interfere. We verify the crosstalk elimination with simultaneous randomized benchmarking, and use a parametrically activated iSWAP interaction to achieve a Bell state preparation fidelity of 98.5% and a √iSWAP gate fidelity of 94.8% obtained via quantum process tomography.

Publisher's Version

DOI:

10.1103/PhysRevApplied.12.054023
Last updated on 07/21/2020

SKIFFS: Superconducting Kinetic Inductance Field-Frequency Sensors for sensitive magnetometry in moderate background magnetic fields

Citation:

A. T. Asfaw, E. I. Kleinbaum, T. M. Hazard, A. Gyenis, A. A. Houck, and S. A. Lyon, “SKIFFS: Superconducting Kinetic Inductance Field-Frequency Sensors for sensitive magnetometry in moderate background magnetic fields,” Applied Physics Letters, vol. 113, pp. 172601, 2018.
SKIFFS: Superconducting Kinetic Inductance Field-Frequency Sensors for sensitive magnetometry in moderate background magnetic fields

ISSN:

00036951

Notes:

We describe sensitive magnetometry using lumped-element resonators fabricated from a supercon- ducting thin film of NbTiN. Taking advantage of the large kinetic inductance of the superconduc- tor, we demonstrate a continuous resonance frequency shift of 27MHz for a change in the magnetic field of 1.8lT within a perpendicular background field of 60mT. By using phase- sensitive readout of microwaves transmitted through the sensors, we measure phase shifts in real time with a sensitivity of 1􏰀/nT. We present measurements of the noise spectral density of the sen- sors and find that their field sensitivity is at least within one to two orders of magnitude of super- conducting quantum interference devices operating with zero background field. Our superconducting kinetic inductance field-frequency sensors enable real-time magnetometry in the presence of moderate perpendicular background fields up to at least 0.2 T. Applications for our sen- sors include the stabilization of magnetic fields in long coherence electron spin resonance measure- ments and quantum computation.

Publisher's Version

DOI:

10.1063/1.5049615
Last updated on 07/21/2020

Nanowire Superinductance Fluxonium Qubit

Citation:

T. M. Hazard, et al., “Nanowire Superinductance Fluxonium Qubit,” Physical Review Letters, vol. 122, pp. 010504, 2019.
Nanowire Superinductance Fluxonium Qubit

Date Published:

Jan

Notes:

Disordered superconducting materials provide a new capability to implement novel circuit designs due to their high kinetic inductance. Here, we realize a fluxonium qubit in which a long NbTiN nanowire shunts a single Josephson junction. We explain the measured fluxonium energy spectrum with a nonperturbative theory accounting for the multimode structure of the device in a large frequency range. Making use of multiphoton Raman spectroscopy, we address forbidden fluxonium transitions and observe multilevel Autler-Townes splitting. Finally, we measure lifetimes of several excited states ranging from T1 = 620 ns to T1 = 20 µs, by applying consecutive π-pulses between multiple fluxonium levels. Our measurements demonstrate that NbTiN is a suitable material for novel superconducting qubit designs.

Publisher's Version

DOI:

10.1103/PhysRevLett.122.010504
Last updated on 07/21/2020

Hyperbolic Lattices in Circuit Quantum Electrodynamics

Citation:

A. J. Kollár, M. Fitzpatrick, and A. A. Houck, “Hyperbolic Lattices in Circuit Quantum Electrodynamics,” Nature, vol. 571, pp. 45-50, 2019.
Hyperbolic Lattices in Circuit Quantum Electrodynamics

ISSN:

1476-4687

Abstract:

After close to two decades of research and development, superconducting circuits have emerged as a rich platform for both quantum computation and quantum simulation. Lattices of superconducting coplanar waveguide (CPW) resonators have been shown to produce artificial materials for microwave photons, where weak interactions can be introduced either via non-linear resonator materials or strong interactions via qubit-resonator coupling. Here, we highlight the previously-overlooked property that these lattice sites are deformable and allow the realization of tight-binding lattices which are unattainable, even in conventional solid-state systems. In particular, we show that networks of CPW resonators can create a new class of materials which constitute regular lattices in an effective hyperbolic space with constant negative curvature. We present numerical simulations of a series of hyperbolic analogs of the kagome lattice which show unusual densities of states with a spectrally-isolated degenerate flat band. We also present a proof-of-principle experimental realization of one of these lattices. This paper represents the first step towards on-chip quantum simulation of materials science and interacting particles in curved space.

Notes:

After close to two decades of research and development, superconducting circuits have emerged as a rich platform for both quantum computation and quantum simulation. Lattices of superconducting coplanar waveguide (CPW) resonators have been shown to produce artificial materials for microwave photons, where weak interactions can be introduced either via non-linear resonator materials or strong interactions via qubit-resonator coupling. Here, we introduce a technique using networks of CPW resonators to create a new class of materials which constitute regular lattices in an effective hyperbolic space with constant negative curvature. We show numerical simulations of a class of hyperbolic analogs of the kagome lattice which show unusual densities of states with a spectrallyisolated degenerate flat band. We also present an experimental realization of one of these lattices, exhibiting the aforementioned band structure. This paper represents the first step towards on-chip quantum simulation of materials science and interacting particles in curved space.

Publisher's Version

DOI:

10.1038/s41586-019-1348-3
Last updated on 07/21/2020

Interacting Qubit-Photon Bound States with Superconducting Circuits

Citation:

N. M. Sundaresan, R. Lundgren, G. Zhu, A. V. Gorshkov, and A. A. Houck, “Interacting Qubit-Photon Bound States with Superconducting Circuits,” Physical Review X, vol. 9, pp. 011021, 2019.
Interacting Qubit-Photon Bound States with Superconducting Circuits

Date Published:

Feb

Notes:

Qubits strongly coupled to a photonic crystal give rise to many exotic physical scenarios, beginning with single and multi-excitation qubit-photon dressed bound states comprising induced spatially localized photonic modes, centered around the qubits, and the qubits themselves. The localization of these states changes with qubit detuning from the band-edge, offering an avenue of in situ control of bound state interaction. Here, we present experimental results from a device with two qubits coupled to a superconducting microwave photonic crystal and realize tunable on-site and inter-bound state interactions. We observe a fourth-order two photon virtual process between bound states indicating strong coupling between the photonic crystal and qubits. Due to their localization-dependent interaction, these states offer the ability to create one-dimensional chains of bound states with tunable and potentially long-range interactions that preserve the qubits’ spatial organization, a key criterion for realization of certain quantum many-body models. The widely tunable, strong and robust interactions demonstrated with this system are promising benchmarks towards realizing larger, more complex systems of bound states.

DOI:

10.1103/PhysRevX.9.011021
Last updated on 07/21/2020

Observation of a Dissipative Phase Transition in a One-Dimensional Circuit QED Lattice

Citation:

M. Fitzpatrick, N. M. Sundaresan, A. C. Y. Li, J. Koch, and A. A. Houck, “Observation of a Dissipative Phase Transition in a One-Dimensional Circuit QED Lattice,” Phys. Rev. X, vol. 7, pp. 011016, 2017.
Observation of a Dissipative Phase Transition in a One-Dimensional Circuit QED Lattice

Date Published:

Feb

Notes:

Condensed matter physics has been driven forward by significant experimental and theoretical progress in the study and understanding of equilibrium phase transitions based on symmetry and topology. However, nonequilibrium phase transitions have remained a challenge, in part due to their complexity in theoretical descriptions and the additional experimental difficulties in systematically controlling systems out of equilibrium. Here, we study a one-dimensional chain of 72 microwave cavities, each coupled to a superconducting qubit, and coherently drive the system into a nonequilibrium steady state. We find experimental evidence for a dissipative phase transition in the system in which the steady state changes dramatically as the mean photon number is increased. Near the boundary between the two observed phases, the system demonstrates bistability, with characteristic switching times as long as 60 ms -- far longer than any of the intrinsic rates known for the system. This experiment demonstrates the power of circuit QED systems for studying nonequilibrium condensed matter physics and paves the way for future experiments exploring nonequilbrium physics with many-body quantum optics.

Publisher's Version

DOI:

10.1103/PhysRevX.7.011016
Last updated on 07/21/2020

Quantum electrodynamics near a photonic bandgap

Citation:

Y. Liu and A. A. Houck, “Quantum electrodynamics near a photonic bandgap,” Nature Physics, vol. 13, pp. 48–52, 2017.
Quantum electrodynamics near a photonic bandgap

Abstract:

Photonic crystals provide an extremely powerful toolset for manipulation of optical dispersion and density of states, and have thus been employed for applications from photon generation to quantum sensing with NVs and atoms. The unique control afforded by these media make them a beautiful, if unexplored, playground for strong coupling quantum electrodynamics, where a single, highly nonlinear emitter hybridizes with the band structure of the crystal. In this work we demonstrate that such hybridization can create localized cavity modes that live within the photonic band-gap, whose localization and spectral properties we explore in detail. We then demonstrate that the coloured vacuum of the photonic crystal can be employed for efficient dissipative state preparation. This work opens exciting prospects for engineering long-range spin models in the circuit QED architecture, as well as new opportunities for dissipative quantum state engineering.

Notes:

Photonic crystals provide an extremely powerful toolset for manipulation of optical dispersion and density of states, and have thus been employed for applications from speelautomaten photon generation to quantum sensing with NVs and atoms. The unique control afforded by these media make them a beautiful, if unexplored, playground for strong coupling quantum electrodynamics, where a single, highly nonlinear emitter hybridizes with the band structure of the crystal. Photonic crystals provide an extremely powerful toolset for manipulation of optical dispersion and density of states, and have thus been employed for applications from photon generation to quantum sensing with NVs and atoms. The unique control afforded by these media make them a beautiful, if unexplored, playground for strong coupling quantum electrodynamics, where a single, highly nonlinear emitter hybridizes with the band structure of the crystal. In this work we demonstrate that such hybridization can create localized cavity modes that live within the photonic band-gap, whose localization and spectral properties we explore in detail. We then demonstrate that the coloured vacuum of the photonic crystal can be employed for efficient dissipative state preparation. This work opens exciting prospects for engineering long-range spin models in the circuit QED architecture, as well as new opportunities for dissipative quantum state engineering.

Publisher's Version

DOI:

10.1038/nphys3834
Last updated on 07/21/2020

Suppression of photon shot noise dephasing in a tunable coupling superconducting qubit

Citation:

G. Zhang, Y. Liu, J. J. Raftery, and A. A. Houck, “Suppression of photon shot noise dephasing in a tunable coupling superconducting qubit,” npj Quantum Information, vol. 3, pp. 1, 2017.
Suppression of photon shot noise dephasing in a tunable coupling superconducting qubit

ISSN:

20566387

Abstract:

We demonstrate the suppression of photon shot noise dephasing in a superconducting qubit by eliminating its dispersive coupling to the readout cavity. This is achieved in a tunable coupling qubit, where the qubit frequency and coupling rate can be controlled independently. We observe that the coherence time approaches twice the relaxation time and becomes less sensitive to thermal photon noise when the dispersive coupling rate is tuned from several MHz to 22 kHz. This work provides a promising building block in circuit quantum electrodynamics that can hold high coherence and be integrated into larger systems.

Notes:

We demonstrate the suppression of photon shot noise dephasing in a superconducting qubit by eliminating its dispersive coupling to the readout cavity. This is achieved in a tunable coupling qubit, where the qubit frequency and coupling rate can be controlled independently. We observe that the coherence time approaches twice the relaxation time and becomes less sensitive to thermal photon noise when the dispersive coupling rate is tuned from several MHz to 22 kHz. This work provides a promising building block in circuit quantum electrodynamics that can hold high coherence and be integrated into larger systems.

Publisher's Version

DOI:

10.1038/s41534-016-0002-2
Last updated on 07/21/2020

Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits

Citation:

A. Chiesa, P. Santini, D. Gerace, J. Raftery, A. A. Houck, and S. Carretta, “Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits,” Scientific Reports, vol. 5, pp. 16036, 2015.
Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits

Abstract:

Resolving quantum many-body problems represents one of the greatest challenges in physics and physical chemistry, due to the prohibitively large computational resources that would be required by using classical computers. A solution has been foreseen by directly simulating the time evolution through sequences of quantum gates applied to arrays of qubits, i.e. by implementing a digital quantum simulator. Superconducting circuits and resonators are emerging as an extremely-promising platform for quantum computation architectures, but a digital quantum simulator proposal that is straightforwardly scalable, universal, and realizable with state-of-the-art technology is presently lacking. Here we propose a viable scheme to implement a universal quantum simulator with hybrid spin-photon qubits in an array of superconducting resonators, which is intrinsically scalable and allows for local control. As representative examples we consider the transverse-field Ising model, a spin-1 Hamiltonian, and the two-dimensional Hubbard model; for these, we numerically simulate the scheme by including the main sources of decoherence. In addition, we show how to circumvent the potentially harmful effects of inhomogeneous broadening of the spin systems.

Notes:

Resolving quantum many-body problems represents one of the greatest challenges in physics and physical chemistry, due to the prohibitively large computational resources that would be required by using classical computers. A solution has been foreseen by directly simulating the time evolution through sequences of quantum gates applied to arrays of qubits, i.e. by implementing a digital quantum simulator. Superconducting circuits and resonators are emerging as an extremely-promising platform for quantum computation architectures, but a digital quantum simulator proposal that is straightforwardly scalable, universal, and realizable with state-of-the-art technology is presently lacking. Here we propose a viable scheme to implement a universal quantum simulator with hybrid spin-photon qubits in an array of superconducting resonators, which is intrinsically scalable and allows for local control. As representative examples we consider the transverse-field Ising model, a spin-1 Hamiltonian, and the two-dimensional Hubbard model; for these, we numerically simulate the scheme by including the main sources of decoherence. In addition, we show how to circumvent the potentially harmful effects of inhomogeneous broadening of the spin systems.

Publisher's Version

DOI:

10.1038/srep16036
Last updated on 07/21/2020

Broadband filters for abatement of spontaneous emission in circuit quantum electrodynamics

Citation:

N. T. Bronn, et al., “Broadband filters for abatement of spontaneous emission in circuit quantum electrodynamics,” Applied Physics Letters, vol. 107, pp. 172601, 2015.
Broadband filters for abatement of spontaneous emission in circuit quantum electrodynamics

ISSN:

00036951

Abstract:

The ability to perform fast, high-fidelity readout of quantum bits (qubits) is essential to the goal of building a quantum computer. However, coupling a fast measurement channel to a superconducting qubit typically also speeds up its relaxation via spontaneous emission. Here we use impedance engineering to design a filter by which photons may easily leave the resonator at the cavity frequency but not at the qubit frequency. We implement this broadband filter in both an on-chip and off-chip configuration.

Notes:

​​​​​​The ability to perform fast, high-fidelity readout of quantum bits (qubits) is essential to the goal of building a quantum computer. However, coupling a fast measurement channel to a superconducting qubit typically also speeds up its relaxation via spontaneous emission. Here we use impedance engineering to design a filter by which photons may easily leave the resonator at the cavity frequency but not at the qubit frequency. We implement this broadband filter in both an on-chip and off-chip configuration.

Publisher's Version

DOI:

10.1063/1.4934867
Last updated on 07/21/2020

Imaging Photon Lattice States by Scanning Defect Microscopy

Citation:

D. L. Underwood, W. E. Shanks, A. C. Y. Li, L. Ateshian, J. Koch, and A. A. Houck, “Imaging Photon Lattice States by Scanning Defect Microscopy,” Phys. Rev. X, vol. 6, pp. 021044, 2016.
Imaging Photon Lattice States by Scanning Defect Microscopy

Date Published:

Jun

Notes:

Microwave photons inside lattices of coupled resonators and superconducting qubits can exhibit surprising matter-like behavior. Realizing such open-system quantum simulators presents an experimental challenge and requires new tools and measurement techniques. Here, we introduce Scanning Defect Microscopy as one such tool and illustrate its use in mapping the normal-mode structure of microwave photons inside a 49-site Kagome lattice of coplanar waveguide resonators. Scanning is accomplished by moving a probe equipped with a sapphire tip across the lattice. This locally perturbs resonator frequencies and induces shifts of the lattice resonance frequencies which we determine by measuring the transmission spectrum. From the magnitude of mode shifts we can reconstruct photon field amplitudes at each lattice site and thus create spatial images of the photon-lattice normal modes.

Publisher's Version

DOI:

10.1103/PhysRevX.6.021044
Last updated on 07/21/2020

Beyond Strong Coupling in a Multimode Cavity

Citation:

N. M. Sundaresan, et al., “Beyond Strong Coupling in a Multimode Cavity,” Physical Review X, vol. 5, pp. 021035, 2015.
Beyond Strong Coupling in a Multimode Cavity

Date Published:

Jun

Notes:

The study of light-matter interaction has seen a resurgence in recent years, stimulated by highly controllable, precise, and modular experiments in cavity quantum electrodynamics (QED). The achievement of strong coupling, where the coupling between a single atom and fundamental cavity mode exceeds the decay rates, was a major milestone that opened the doors to a multitude of new investigations. Here we introduce multimode strong coupling (MMSC), where the coupling is comparable to the free spectral range (FSR) of the cavity, i.e. the rate at which a qubit can absorb a photon from the cavity is comparable to the round trip transit rate of a photon in the cavity. We realize, via the circuit QED architecture, the first experiment accessing the MMSC regime, and report remarkably widespread and structured resonance fluorescence, whose origin extends beyond cavity enhancement of sidebands. Our results capture complex multimode, multiphoton processes, and the emergence of ultranarrow linewidths. Beyond the novel phenomena presented here, MMSC opens a major new direction in the exploration of light-matter interactions.

Publisher's Version

DOI:

10.1103/PhysRevX.5.021035
Last updated on 07/21/2020

Observation of a Dissipation-Induced Classical to Quantum Transition

Citation:

J. Raftery, D. Sadri, S. Schmidt, H. E. Türeci, and A. A. Houck, “Observation of a Dissipation-Induced Classical to Quantum Transition,” Phys. Rev. X, vol. 4, pp. 031043, 2014.
Observation of a Dissipation-Induced Classical to Quantum Transition

Date Published:

Sep

Notes:

The emergence of non-trivial structure in many-body physics has been a central topic of research bearing on many branches of science. Important recent work has explored the non-equilibrium quantum dynamics of closed many-body systems. Photonic systems offer a unique platform for the study of open quantum systems. We report here the experimental observation of a novel dissipation driven dynamical localization transition of strongly correlated photons in an extended superconducting circuit. Monitoring the homodyne signal reveals this transition to be from a regime of classical oscillations into a macroscopically self-trapped state manifesting revivals, a fundamentally quantum phenomenon. This experiment also demonstrates a new class of scalable quantum simulators with well controlled coherent and dissipative dynamics suited to the study of quantum many-body phenomena out of equilibrium.

Publisher's Version

DOI:

10.1103/PhysRevX.4.031043
Last updated on 07/21/2020

Time-reversal symmetrization of spontaneous emission for quantum state transfer

Citation:

S. J. Srinivasan, et al., “Time-reversal symmetrization of spontaneous emission for quantum state transfer,” Physical Review A, vol. 89, pp. 033857, 2014.
Time-reversal symmetrization of spontaneous emission for quantum state transfer

Date Published:

Mar

Notes:

We demonstrate the ability to control the spontaneous emission from a superconducting qubit coupled to a cavity. The time domain profile of the emitted photon is shaped into a symmetric truncated exponential. The experiment is enabled by a qubit coupled to a cavity, with a coupling strength that can be tuned in tens of nanoseconds while maintaining a constant dressed state emission frequency. Symmetrization of the photonic wave packet will enable use of photons as flying qubits for transfering the quantum state between atoms in distant cavities.

Publisher's Version

DOI:

10.1103/PhysRevA.89.033857
Last updated on 07/21/2020

A scanning transmon qubit for strong coupling circuit quantum electrodynamics

Citation:

W. E. Shanks, D. L. Underwood, and A. A. Houck, “A scanning transmon qubit for strong coupling circuit quantum electrodynamics,” Nature Communications, vol. 4, no. May, pp. 1–6, 2013.
A scanning transmon qubit for strong coupling circuit quantum electrodynamics

ISSN:

20411723

Abstract:

Like a quantum computer designed for a particular class of problems, a quantum simulator enables quantitative modeling of quantum systems that is computationally intractable with a classical computer. Quantum simulations of quantum many-body systems have been performed using ultracold atoms and trapped ions among other systems. Superconducting circuits have recently been investigated as an alternative system in which microwave photons confined to a lattice of coupled resonators act as the particles under study with qubits coupled to the resonators producing effective photon-photon interactions. Such a system promises insight into the nonequilibrium physics of interacting bosons but new tools are needed to understand this complex behavior. Here we demonstrate the operation of a scanning transmon qubit and propose its use as a local probe of photon number within a superconducting resonator lattice. We map the coupling strength of the qubit to a resonator on a separate chip and show that the system reaches the strong coupling regime over a wide scanning area.

Notes:

Like a quantum computer designed for a particular class of problems, a quantum simulator enables quantitative modeling of quantum systems that is computationally intractable with a classical computer. Quantum simulations of quantum many-body systems have been performed using ultracold atoms and trapped ions among other systems. Superconducting circuits have recently been investigated as an alternative system in which microwave photons confined to a lattice of coupled resonators act as the particles under study with qubits coupled to the resonators producing effective photon-photon interactions. Such a system promises insight into the nonequilibrium physics of interacting bosons but new tools are needed to understand this complex behavior. Here we demonstrate the operation of a scanning transmon qubit and propose its use as a local probe of photon number within a superconducting resonator lattice. We map the coupling strength of the qubit to a resonator on a separate chip and show that the system reaches the strong coupling regime over a wide scanning area.

Publisher's Version

DOI:

10.1038/ncomms2991
Last updated on 07/10/2019

Circuit quantum electrodynamics with a spin qubit

Citation:

K. D. Petersson, et al., “Circuit quantum electrodynamics with a spin qubit,” Nature, vol. 490, no. 7420, pp. 380–383, 2012.
Circuit quantum electrodynamics with a spin qubit

ISSN:

00280836

Abstract:

Circuit quantum electrodynamics allows spatially separated superconducting qubits to interact via a "quantum bus", enabling two-qubit entanglement and the implementation of simple quantum algorithms. We combine the circuit quantum electrodynamics architecture with spin qubits by coupling an InAs nanowire double quantum dot to a superconducting cavity. We drive single spin rotations using electric dipole spin resonance and demonstrate that photons trapped in the cavity are sensitive to single spin dynamics. The hybrid quantum system allows measurements of the spin lifetime and the observation of coherent spin rotations. Our results demonstrate that a spin-cavity coupling strength of 1 MHz is feasible.

Notes:

Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a ‘quantum bus’, making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge–cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin–orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge–cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin–cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.

Publisher's Version

DOI:

10.1038/nature11559
Last updated on 07/10/2019
  •  
  • 1 of 3
  • »