Publications

Anomalous Hall effects of light and chiral edge modes on the Kagomé lattice

Citation:

A. Petrescu, A. A. Houck, and K. L. Hur, “Anomalous Hall effects of light and chiral edge modes on the Kagomé lattice,” Phys. Rev. A, vol. 86, pp. 053804, 2012.
Anomalous Hall effects of light and chiral edge modes on the Kagomé lattice

Date Published:

Nov

Notes:

We theoretically investigate a photonic Kagome lattice which can be realized in microwave cavity arrays using current technology. The Kagome lattice exhibits an exotic band structure with three bands one of which can be made completely flat. The presence of artificial gauge fields allows to emulate topological phases and induce chiral edge modes which can coexist inside the energy gap with the flat band that is topologically trivial. By tuning the artificial fluxes or in the presence of disorder, the flat band can also acquire a bandwidth in energy allowing the coexistence between chiral edge modes and bulk extended states; in this case the chiral modes become fragile towards scattering into the bulk. The photonic system then exhibits equivalents of both a quantum Hall effect without Landau levels, and an anomalous Hall effect characterized by a non-quantized Chern number. We discuss experimental observables such as local density of states and edge currents. We show how synthetic uniform magnetic fields can be engineered, which allows an experimental probe of Landau levels in the photonic Kagome lattice. We then draw on semiclassical Boltzmann equations for transport to devise a method to measure Berry's phases around loops in the Brillouin zone. The method is based solely on wavepacket interference and can be used to determine band Chern numbers or the photonic equivalent of the anomalous Hall response. We demonstrate the robustness of these measurements towards on-site and gauge-field disorder. We also show the stability of the anomalous quantum Hall phase for nonlinear cavities and for (artificial) atom-photon interactions.

Publisher's Version

DOI:

10.1103/PhysRevA.86.053804
Last updated on 07/10/2019

On-chip quantum simulation with superconducting circuits

Citation:

A. A. Houck, H. E. Türeci, and J. Koch, “On-chip quantum simulation with superconducting circuits,” Nature Physics, vol. 8, no. 4, pp. 292–299, 2012.
On-chip quantum simulation with superconducting circuits

ISSN:

17452473

Abstract:

Using a well-controlled quantum system to simulate complex quantum matter is an idea that has been around for 30 years and put into practice in systems of ultracold atoms for more than a decade. Much recent excitement has focused on a new implementation of quantum simulators using superconducting circuits, where conventional microchip fabrication can be used to take design concepts to experimental reality, quickly and flexibly. Because the quantum 'particles' in these simulators are circuit excitations rather than physical particles subject to conservation laws, superconducting simulators provide a complement to ultracold atoms by naturally accessing non-equilibrium physics. Here, we review the recent wealth of theoretical explorations and experimental prospects of realizing these new devices. © 2012 Macmillan Publishers Limited. All rights reserved.

Notes:

Using a well-controlled quantum system to simulate complex quantum matter is an idea that has been around for 30 years and put into practice in systems of ultracold atoms for more than a decade. Much recent excitement has focused on a new implementation of quantum simulators using superconducting circuits, where conventional microchip fabrication can be used to take design concepts to experimental reality, quickly and flexibly. Because the quantum ‘particles’ in these simulators are circuit excitations rather than physical particles subject to conservation laws, superconducting simulators provide a complement to ultracold atoms by naturally accessing non-equilibrium physics. Here, we review the recent wealth of theoretical explorations and experimental prospects of realizing these new devices.

Publisher's Version

DOI:

10.1038/nphys2251
Last updated on 07/10/2019

Low-disorder microwave cavity lattices for quantum simulation with photons

Citation:

D. L. Underwood, W. E. Shanks, J. Koch, and A. A. Houck, “Low-disorder microwave cavity lattices for quantum simulation with photons,” Phys. Rev. A, vol. 86, pp. 023837, 2012.
Low-disorder microwave cavity lattices for quantum simulation with photons

Date Published:

Aug

Notes:

We assess experimentally the suitability of coupled transmission line resonators for studies of quantum phase transitions of light. We have measured devices with low photon hopping rates t/2pi = 0.8MHz to quantify disorder in individual cavity frequencies. The observed disorder is consistent with small imperfections in fabrication. We studied the dependence of the disorder on transmission line geometry and used our results to fabricate devices with disorder less than two parts in 10^4.

Publisher's Version

DOI:

10.1103/PhysRevA.86.023837
Last updated on 07/10/2019

Superconducting coplanar waveguide resonators for low temperature pulsed electron spin resonance spectroscopy

Citation:

H. Malissa, D. I. Schuster, A. M. Tyryshkin, A. A. Houck, and S. A. Lyon, “Superconducting coplanar waveguide resonators for low temperature pulsed electron spin resonance spectroscopy,” Review of Scientific Instruments, vol. 84, no. 2, pp. 1–4, 2013.
Superconducting coplanar waveguide resonators for low temperature pulsed electron spin resonance spectroscopy

ISSN:

00346748

Abstract:

We discuss the design and implementation of thin film superconducting coplanar waveguide micro- resonators for pulsed ESR experiments. The performance of the resonators with P doped Si epilayer samples is compared to waveguide resonators under equivalent conditions. The high achievable filling factor even for small sized samples and the relatively high Q-factor result in a sensitivity that is superior to that of conventional waveguide resonators, in particular to spins close to the sample surface. The peak microwave power is on the order of a few microwatts, which is compatible with measurements at ultra low temperatures. We also discuss the effect of the nonuniform microwave magnetic field on the Hahn echo power dependence.

Notes:

We discuss the design and implementation of thin film superconducting coplanar waveguide micro- resonators for pulsed ESR experiments. The performance of the resonators with P doped Si epilayer samples is compared to waveguide resonators under equivalent conditions. The high achievable filling factor even for small sized samples and the relatively high Q-factor result in a sensitivity that is superior to that of conventional waveguide resonators, in particular to spins close to the sample surface. The peak microwave power is on the order of a few microwatts, which is compatible with measurements at ultra low temperatures. We also discuss the effect of the nonuniform microwave magnetic field on the Hahn echo power dependence.

DOI:

10.1063/1.4792205
Last updated on 07/10/2019

Coherent control of a superconducting qubit with dynamically tunable qubit-cavity coupling

Citation:

A. J. Hoffman, S. J. Srinivasan, J. M. Gambetta, and A. A. Houck, “Coherent control of a superconducting qubit with dynamically tunable qubit-cavity coupling,” Phys. Rev. B, vol. 84, pp. 184515, 2011.
Coherent control of a superconducting qubit with dynamically tunable qubit-cavity coupling

Date Published:

Nov

Notes:

We demonstrate coherent control and measurement of a superconducting qubit coupled to a superconducting coplanar waveguide resonator with a dynamically tunable qubit-cavity coupling strength. Rabi oscillations are measured for several coupling strengths showing that the qubit transition can be turned off by a factor of more than 1500. We show how the qubit can still be accessed in the off state via fast flux pulses. We perform pulse delay measurements with synchronized fast flux pulses on the device and observe T1 and T2 times of 1.6 and 1.9 μs, respectively. This work demonstrates how this qubit can be incorporated into quantum architectures.

Publisher's Version

DOI:

10.1103/PhysRevB.84.184515
Last updated on 07/10/2019

Dispersive Photon Blockade in a Superconducting Circuit

Citation:

A. J. Hoffman, et al., “Dispersive Photon Blockade in a Superconducting Circuit,” Phys. Rev. Lett. vol. 107, pp. 053602, 2011.
Dispersive Photon Blockade in a Superconducting Circuit

Date Published:

Jul

Notes:

Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.

Publisher's Version

DOI:

10.1103/PhysRevLett.107.053602
Last updated on 07/10/2019

Tunable Coupling in Circuit Quantum Electrodynamics Using a Superconducting Charge Qubit with a $V$-Shaped Energy Level Diagram

Citation:

S. J. Srinivasan, A. J. Hoffman, J. M. Gambetta, and A. A. Houck, “Tunable Coupling in Circuit Quantum Electrodynamics Using a Superconducting Charge Qubit with a $V$-Shaped Energy Level Diagram,” Phys. Rev. Lett. vol. 106, pp. 083601, 2011.
Tunable Coupling in Circuit Quantum Electrodynamics Using a Superconducting Charge Qubit with a $V$-Shaped Energy Level Diagram

Date Published:

Feb

Notes:

We introduce a new type of superconducting charge qubit that has aV-shaped energy spectrum and uses quantum interference to provide independently tunable qubit energy and coherent coupling to a superconducting cavity. Dynamic access to the strong coupling regime is demonstrated by tuning the coupling strength from less than 200 kHz to greater than 40 MHz. This tunable coupling can be used to protect the qubit from cavity-induced relaxation and avoid unwanted qubit-qubit interactions in a multiqubit system.

Publisher's Version

DOI:

10.1103/PhysRevLett.106.083601
Last updated on 07/10/2019

Superconducting Qubit with Purcell Protection and Tunable Coupling

Citation:

J. M. Gambetta, A. A. Houck, and A. Blais, “Superconducting Qubit with Purcell Protection and Tunable Coupling,” Phys. Rev. Lett. vol. 106, pp. 030502, 2011.
Superconducting Qubit with Purcell Protection and Tunable Coupling

Date Published:

Jan

Notes:

We present a superconducting qubit for the circuit quantum electrodynamics architecture that has a tunable qubit-resonator coupling strengthg. This coupling can be tuned from zero to values that are comparable with other superconducting qubits. At g=0, the qubit is in a decoherence-free subspace with respect to spontaneous emission induced by the Purcell effect. Furthermore, we show that in this decoherence-free subspace, the state of the qubit can still be measured by either a dispersive shift on the resonance frequency of the resonator or by a cycling-type measurement.

Publisher's Version

DOI:

10.1103/PhysRevLett.106.030502
Last updated on 07/10/2019

Quantum non-demolition detection of single microwave photons in a circuit

Citation:

B. R. Johnson, et al., “Quantum non-demolition detection of single microwave photons in a circuit,” Nature Physics, vol. 6, no. 9, pp. 663–667, 2010.
Quantum non-demolition detection of single microwave photons in a circuit

ISSN:

17452481

Abstract:

Thorough control of quantum measurement is key to the development of quantum information technologies. Many measurements are destructive, removing more information from the system than they obtain. Quantum non-demolition (QND) measurements allow repeated measurements that give the same eigenvalue. They could be used for several quantum information processing tasks such as error correction, preparation by measurement, and one-way quantum computing. Achieving QND measurements of photons is especially challenging because the detector must be completely transparent to the photons while still acquiring information about them. Recent progress in manipulating microwave photons in superconducting circuits has increased demand for a QND detector which operates in the gigahertz frequency range. Here we demonstrate a QND detection scheme which measures the number of photons inside a high quality-factor microwave cavity on a chip. This scheme maps a photon number onto a qubit state in a single-shot via qubit-photon logic gates. We verify the operation of the device by analyzing the average correlations of repeated measurements, and show that it is 90% QND. It differs from previously reported detectors because its sensitivity is strongly selective to chosen photon number states. This scheme could be used to monitor the state of a photon-based memory in a quantum computer.

Notes:

Thorough control of quantum measurement is key to the development of quantum information technologies. Many measurements are destructive, removing more information from the system than they obtain. Quantum non-demolition (QND) measurements allow repeated measurements that give the same eigenvalue. They could be used for several quantum information processing tasks such as error correction, preparation by measurement, and one-way quantum computing. Achieving QND measurements of photons is especially challenging because the detector must be completely transparent to the photons while still acquiring information about them. Recent progress in manipulating microwave photons in superconducting circuits has increased demand for a QND detector which operates in the gigahertz frequency range. Here we demonstrate a QND detection scheme which measures the number of photons inside a high quality-factor microwave cavity on a chip. This scheme maps a photon number onto a qubit state in a single-shot via qubit-photon logic gates. We verify the operation of the device by analyzing the average correlations of repeated measurements, and show that it is 90% QND. It differs from previously reported detectors because its sensitivity is strongly selective to chosen photon number states. This scheme could be used to monitor the state of a photon-based memory in a quantum computer.

Publisher's Version

DOI:

10.1038/nphys1710
Last updated on 07/10/2019

Fast reset and suppressing spontaneous emission of a superconducting qubit

Citation:

M. D. Reed, et al., “Fast reset and suppressing spontaneous emission of a superconducting qubit,” Applied Physics Letters, vol. 96, no. 20, pp. 203110, 2010.
Fast reset and suppressing spontaneous emission of a superconducting qubit

Notes:

Spontaneous emission through a coupled cavity can be a significant decay channel for qubits in circuit QED. We present a new circuit design that effectively eliminates spontaneous emission due to the Purcell effect while maintaining strong coupling to a low Q cavity. Excellent agreement over a wide range in frequency is found between measured qubit relaxation times and the predictions of a circuit model. Using fast (nanosecond time-scale) flux biasing of the qubit, we demonstrate in-situ control of qubit lifetime over a factor of 50. We realize qubit reset with 99.9% fidelity in 120 ns.

Publisher's Version

DOI:

10.1063/1.3435463
Last updated on 07/09/2019

Time-reversal-symmetry breaking in circuit-QED-based photon lattices

Citation:

J. Koch, A. A. Houck, K. L. Hur, and S. M. Girvin, “Time-reversal-symmetry breaking in circuit-QED-based photon lattices,” Phys. Rev. A, vol. 82, pp. 043811, 2010.
Time-reversal-symmetry breaking in circuit-QED-based photon lattices

Date Published:

Oct

Notes:

Breaking time-reversal symmetry is a prerequisite for accessing certain interesting many-body states such as fractional quantum Hall states. For polaritons, charge neutrality prevents magnetic fields from providing a direct symmetry-breaking mechanism and, similar to the situation in ultracold atomic gases, an effective magnetic field has to be synthesized. We show that in the circuit-QED architecture, this can be achieved by inserting simple superconducting circuits into the resonator junctions.

Publisher's Version

DOI:

10.1103/PhysRevA.82.043811
Last updated on 07/09/2019

Nonlinear response of the vacuum Rabi resonance

Citation:

L. S. Bishop, et al., “Nonlinear response of the vacuum Rabi resonance,” Nature Physics, vol. 5, no. 2, pp. 105–109, 2009.
Nonlinear response of the vacuum Rabi resonance

ISSN:

17452481

Abstract:

On the level of single atoms and photons, the coupling between atoms and the electromagnetic field is typically very weak. By employing a cavity to confine the field, the strength of this interaction can be increased many orders of magnitude to a point where it dominates over any dissipative process. This strong-coupling regime of cavity quantum electrodynamics has been reached for real atoms in optical cavities, and for artificial atoms in circuit QED and quantum-dot systems. A signature of strong coupling is the splitting of the cavity transmission peak into a pair of resolvable peaks when a single resonant atom is placed inside the cavity - an effect known as vacuum Rabi splitting. The circuit QED architecture is ideally suited for going beyond this linear response effect. Here, we show that increasing the drive power results in two unique nonlinear features in the transmitted heterodyne signal: the supersplitting of each vacuum Rabi peak into a doublet, and the appearance of additional peaks with the characteristic sqrt(n) spacing of the Jaynes-Cummings ladder. These constitute direct evidence for the coupling between the quantized microwave field and the anharmonic spectrum of a superconducting qubit acting as an artificial atom.

Notes:

On the level of single atoms and photons, the coupling between atoms and the electromagnetic field is typically very weak. By using a cavity to confine the field, the strength of this interaction can be increased by many orders of magnitude, to a point where it dominates over any dissipative process. This strong-coupling regime of cavity quantum electrodynamics has been reached for real atoms in optical cavities, and for artificial atoms in circuit quantum electrodynamics and quantum dot systems.

Publisher's Version

DOI:

10.1038/nphys1154
Last updated on 07/09/2019

Life after charge noise: recent results with transmon qubits

Citation:

A. A. Houck, J. Koch, M. H. Devoret, S. M. Girvin, and R. J. Schoelkopf, “Life after charge noise: recent results with transmon qubits,” Quantum Information Processing, vol. 8, no. 2, pp. 105–115, 2009.
Life after charge noise: recent results with transmon qubits

Date Published:

Jun

ISSN:

1573-1332

Abstract:

We review the main theoretical and experimental results for the transmon, a superconducting charge qubit derived from the Cooper pair box. The increased ratio of the Josephson to charging energy results in an exponential suppression of the transmon's sensitivity to 1/f charge noise. This has been observed experimentally and yields homogeneous broadening, negligible pure dephasing, and long coherence times of up to 3 $μ$s. Anharmonicity of the energy spectrum is required for qubit operation, and has been proven to be sufficient in transmon devices. Transmons have been implemented in a wide array of experiments, demonstrating consistent and reproducible results in very good agreement with theory.

Notes:

We review the main theoretical and experimental results for the transmon, a superconducting charge qubit derived from the Cooper pair box. The increased ratio of the Josephson to charging energy results in an exponential suppression of the transmon’s sensitivity to 1/f charge noise. This has been observed experimentally and yields homogeneous broadening, negligible pure dephasing, and long coherence times of up to 3 μs. Anharmonicity of the energy spectrum is required for qubit operation, and has been proven to be sufficient in transmon devices. Transmons have been implemented in a wide array of experiments, demonstrating consistent and reproducible results in very good agreement with theory.

Publisher's Version

DOI:

10.1007/s11128-009-0100-6
Last updated on 07/09/2019

Proposal for generating and detecting multi-qubit GHZ states in circuit QED

Citation:

L. S. Bishop, et al., “Proposal for generating and detecting multi-qubit GHZ states in circuit QED,” New Journal of Physics, vol. 11, no. 7, pp. 073040, 2009.
Proposal for generating and detecting multi-qubit GHZ states in circuit QED

Date Published:

jul

Abstract:

We propose methods for the preparation and entanglement detection of multi-qubit Greenberger–Horne–Zeilinger (GHZ) states in circuit quantum electrodynamics. Using quantum trajectory simulations appropriate for the situation of a weak continuous measurement, we show that the joint dispersive readout of several qubits can be utilized for the probabilistic production of high-fidelity GHZ states. When employing a nonlinear filter on the recorded homodyne signal, the selected states are found to exhibit values of the Bell–Mermin operator exceeding 2 under realistic conditions. We discuss the potential of the dispersive readout to demonstrate a violation of the Mermin bound, and present a measurement scheme avoiding the necessity for full detector tomography.

Notes:

We propose methods for the preparation and entanglement detection of multi-qubit Greenberger–Horne–Zeilinger (GHZ) states in circuit quantum electrodynamics. Using quantum trajectory simulations appropriate for the situation of a weak continuous measurement, we show that the joint dispersive readout of several qubits can be utilized for the probabilistic production of high-fidelity GHZ states. When employing a nonlinear filter on the recorded homodyne signal, the selected states are found to exhibit values of the Bell–Mermin operator exceeding 2 under realistic conditions. We discuss the potential of the dispersive readout to demonstrate a violation of the Mermin bound, and present a measurement scheme avoiding the necessity for full detector tomography.

Publisher's Version

DOI:

10.1088/1367-2630/11/7/073040
Last updated on 07/09/2019

Randomized Benchmarking and Process Tomography for Gate Errors in a Solid-State Qubit

Citation:

J. M. Chow, et al., “Randomized Benchmarking and Process Tomography for Gate Errors in a Solid-State Qubit,” Phys. Rev. Lett. vol. 102, pp. 090502, 2009.
Randomized Benchmarking and Process Tomography for Gate Errors in a Solid-State Qubit

Date Published:

Mar

Notes:

We present measurements of single-qubit gate errors for a superconducting qubit. Results from quantum process tomography and randomized benchmarking are compared with gate errors obtained from a double π pulse experiment. Randomized benchmarking reveals a minimum average gate error of 1.1±0.3% and a simple exponential dependence of fidelity on the number of gates. It shows that the limits on gate fidelity are primarily imposed by qubit decoherence, in agreement with theory.

Publisher's Version

DOI:

10.1103/PhysRevLett.102.090502
Last updated on 07/09/2019

Controlling the Spontaneous Emission of a Superconducting Transmon Qubit

Citation:

A. A. Houck, et al., “Controlling the Spontaneous Emission of a Superconducting Transmon Qubit,” Phys. Rev. Lett. vol. 101, pp. 080502, 2008.
Controlling the Spontaneous Emission of a Superconducting Transmon Qubit

Date Published:

Aug

Notes:

We present a detailed characterization of coherence in seven transmon qubits in a circuit QED architecture. We find that spontaneous emission rates are strongly influenced by far off-resonant modes of the cavity and can be understood within a semiclassical circuit model. A careful analysis of the spontaneous qubit decay into a microwave transmission-line cavity can accurately predict the qubit lifetimes over two orders of magnitude in time and more than an octave in frequency. Coherence times T1 and T2* of more than a microsecond are reproducibly demonstrated.

Publisher's Version

DOI:

10.1103/PhysRevLett.101.080502
Last updated on 07/09/2019

Suppressing charge noise decoherence in superconducting charge qubits

Citation:

J. A. Schreier, et al., “Suppressing charge noise decoherence in superconducting charge qubits,” Phys. Rev. B, vol. 77, pp. 180502, 2008.
Suppressing charge noise decoherence in superconducting charge qubits

Date Published:

May

Notes:

We present an experimental realization of the transmon qubit, an improved superconducting charge qubit derived from the Cooper pair box. We experimentally verify the predicted exponential suppression of sensitivity to 1/f charge noise [J. Koch et al., Phys. Rev. A 76, 042319 (2007)]. This removes the leading source of dephasing in charge qubits, resulting in homogenously broadened transitions with relaxation and dephasing times in the microsecond range.

Publisher's Version

DOI:

10.1103/PhysRevB.77.180502
Last updated on 07/09/2019

Quantum trajectory approach to circuit QED: Quantum jumps and the Zeno effect

Citation:

J. Gambetta, A. Blais, M. Boissonneault, A. A. Houck, D. I. Schuster, and S. M. Girvin, “Quantum trajectory approach to circuit QED: Quantum jumps and the Zeno effect,” Phys. Rev. A, vol. 77, pp. 012112, 2008.
Quantum trajectory approach to circuit QED: Quantum jumps and the Zeno effect

Date Published:

Jan

Notes:

We present a theoretical study of a superconducting charge qubit dispersively coupled to a transmission line resonator. Starting from a master equation description of this coupled system and using a polaron transformation, we obtain an exact effective master equation for the qubit. We then use quantum trajectory theory to investigate the measurement of the qubit by continuous homodyne measurement of the resonator out-field. Using the same porlaron transformation, a stochastic master equation for the conditional state of the qubit is obtained.

Publisher's Version

DOI:

10.1103/PhysRevA.77.012112
Last updated on 07/09/2019

Charge-insensitive qubit design derived from the Cooper pair box

Citation:

J. Koch, et al., “Charge-insensitive qubit design derived from the Cooper pair box,” Phys. Rev. A, vol. 76, pp. 042319, 2007.
Charge-insensitive qubit design derived from the Cooper pair box

Date Published:

Oct

Notes:

Short dephasing times pose one of the main challenges in realizing a quantum computer. Different approaches have been devised to cure this problem for superconducting qubits, a prime example being the operation of such devices at optimal working points, so-called "sweet spots." This latter approach led to significant improvement of T2 times in Cooper pair box qubits [D. Vion et al., Science 296, 886 (2002)].

Publisher's Version

DOI:

10.1103/PhysRevA.76.042319
Last updated on 07/09/2019

Coupling superconducting qubits via a cavity bus

Citation:

J. Majer, et al., “Coupling superconducting qubits via a cavity bus,” Nature, vol. 449, pp. 443, 2007.
Coupling superconducting qubits via a cavity bus

Date Published:

sep

Notes:

Superconducting circuits are promising candidates for constructing quantum bits (qubits) in a quantum computer; single-qubit operations are now routine, and several examples of two qubit interactions and gates having been demonstrated. These experiments show that two nearby qubits can be readily coupled with local interactions. Performing gates between an arbitrary pair of distant qubits is highly desirable for any quantum computer architecture, but has not yet been demonstrated. An efficient way to achieve this goal is to couple the qubits to a quantum bus, which distributes quantum information among the qubits. Here we show the implementation of such a quantum bus, using microwave photons confined in a transmission line cavity, to couple two superconducting qubits on opposite sides of a chip. The interaction is mediated by the exchange of virtual rather than real photons, avoiding cavity induced loss. Using fast control of the qubits to switch the coupling effectively on and off, we demonstrate coherent transfer of quantum states between the qubits. The cavity is also used to perform multiplexed control and measurement of the qubit states. This approach can be expanded to more than two qubits, and is an attractive architecture for quantum information processing on a chip.

Publisher's Version

Last updated on 07/09/2019

Generating single microwave photons in a circuit

Citation:

A. A. Houck, et al., “Generating single microwave photons in a circuit,” Nature, vol. 449, pp. 328, 2007.
Generating single microwave photons in a circuit

Date Published:

sep

Notes:

Microwaves have widespread use in classical communication technologies, from long-distance broadcasts to short-distance signals within a computer chip. Like all forms of light, microwaves, even those guided by the wires of an integrated circuit, consist of discrete photons. To enable quantum communication between distant parts of a quantum computer, the signals must also be quantum, consisting of single photons, for example. However, conventional sources can generate only classical light, not single photons.

Publisher's Version

Last updated on 07/09/2019

Resolving photon number states in a superconducting circuit

Resolving photon number states in a superconducting circuit

Notes:

Electromagnetic signals are always composed of photons, although in the circuit domain those signals are carried as voltages and currents on wires, and the discreteness of the photon’s energy is usually not evident. However, by coupling a superconducting quantum bit (qubit) to signals on a microwave transmission line, it is possible to construct an integrated circuit in which the presence or absence of even a single photon can have a dramatic effect.

Publisher's Version

Kondo Effect in the Presence of Magnetic Impurities

Citation:

H. B. Heersche, et al., “Kondo Effect in the Presence of Magnetic Impurities,” Phys. Rev. Lett. vol. 96, pp. 017205, 2006.
Kondo Effect in the Presence of Magnetic Impurities

Date Published:

Jan

Notes:

We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to a RKKY interaction between the spin of the dot and the static spins of the impurities. A magnetic field restores the single Kondo peak in the case of an antiferromagnetic RKKY interaction. This system provides a new platform to study Kondo and RKKY interactions in metals at the level of a single spin.

Publisher's Version

DOI:

10.1103/PhysRevLett.96.017205
Last updated on 07/09/2019

Kondo Effect in Electromigrated Gold Break Junctions

Citation:

A. A. Houck, J. Labaziewicz, E. K. Chan, J. A. Folk, and I. L. Chuang, “Kondo Effect in Electromigrated Gold Break Junctions,” Nano Letters, 2005.
Kondo Effect in Electromigrated Gold Break Junctions

Notes:

We present gate-dependent transport measurements of Kondo impurities in bare gold break junctions, generated with high yield using an electromigration process that is actively controlled. Thirty percent of measured devices show zero-bias conductance peaks. Temperature dependence suggests Kondo temperatures 7 K. The peak splitting in magnetic field is consistent with theoretical predictions for g = 2, though in many devices the splitting is offset from 2gμBby a fixed energy

Last updated on 07/09/2019

Focusing inside negative index materials

Citation:

J. B. Brock, A. A. Houck, and I. L. Chuang, “Focusing inside negative index materials,” Applied Physics Letters, 2004.
Focusing inside negative index materials

Notes:

Two key theoretical predictions for flat negative index lenses are that thicker lenses should have both internal and external foci, and that these foci should move linearly with small deviations in frequency. Two-dimensional electric field profiles of microwave transmission through rectangular slabs of composite wire and split-ring resonator material are presented. By scanning inside and outside the material, both internal and external foci are revealed. The power concentration around the internal focus is shown to have a negative curvature, consistent with the theoretical predictions.

Experimental Observations of a Left-Handed Material That Obeys Snell’s Law

Citation:

A. A. Houck, J. B. Brock, and I. L. Chuang, “Experimental Observations of a Left-Handed Material That Obeys Snell’s Law,” Physics Review Letters, 2003.
Experimental Observations of a Left-Handed Material That Obeys Snell’s Law

Notes:

We measure two-dimensional profiles of collimated microwave beams transmitted through composite wire and split-ring resonator prisms. Prior experiments suggest these structures have a negative index of refraction, though these claims have been questioned. Our 2D measurements demonstrate that transmission obeys Snell’s law with a negative index, confirming the refractive nature of this signal and refuting alternatives posed in the criticisms. In addition, we present preliminary evidence that a flat rectangular slab of this material can focus power from a point source.

Publisher's Version

Last updated on 07/08/2019

Improving Quantum Hardware: Building New Superconducting Qubits and Couplers

Improving Quantum Hardware: Building New Superconducting Qubits and Couplers

Thesis Type:

PhD

Abstract:

Over the past 10 years, improvements to the fundamental components in supercon- ducting qubits and the realization of novel circuit topologies have increased the life- times of qubits and catapulted this architecture to become one of the leading hardware platforms for universal quantum computation. Despite the progress that has been made in increasing the lifetime of the charge qubit by almost six orders of magnitude, further improvements must be made to climb over the threshold for fault tolerant quantum computation. Two complimentary approaches towards achieving this goal are investigating and improving upon existing qubit designs, and looking for new types of superconducting qubits which would offer some intrinsic improvements over existing designs. This thesis will explore both of these directions through a detailed study of new materials, circuit designs, and coupling schemes for superconducting qubits. In the first experiment, we explore the use of disordered superconducting films, specifically Niobium Titanium Nitride, as the inductive element in a fluxonium qubit and measure the loss mechanisms limiting the qubit lifetime. In the second experiment, we work towards the experimental realization of the 0 − π qubit archi- tecture, which offers the promise of intrinsic protection in lifetime and decoherence compared to existing superconducting qubits. In the final experiment, we design and measure a two qubit device where the static σz ⊗ σz crosstalk between the two qubits is eliminated via destructive interference. The use of multiple coupling elements re- moves the σz ⊗ σz crosstalk while maintaining the large σz ⊗ σx interaction needed to perform two qubit gates.

Publisher's Version

See also: Theses
Last updated on 02/02/2021

Microwave Cavity Lattices for Quantum Simulation with Photons

Microwave Cavity Lattices for Quantum Simulation with Photons

Thesis Type:

PhD

Abstract:

Historically our understanding of the microscopic world has been impeded by limitations in systems that behave classically. Even today, understanding simple problems in quantum mechanics remains a dicult task both computationally and experimentally. As a means of overcoming these classical limitations, the idea of using a controllable quantum system to simulate a less controllable quantum system has been proposed. This concept is known as quantum simulation and is the origin of the ideas behind quantum computing. In this thesis, experiments have been conducted that address the feasibility of using devices with a circuit quantum electrodynamics (cQED) architecture as a quantum simulator. In a cQED device, a superconducting qubit is capacitively coupled to a superconducting resonator resulting in coherent quantum behavior of the qubit when it interacts with photons inside the resonator. It has been shown theoretically that by forming a lattice of cQED elements, dierent quantum phases of photons will exist for dierent system parameters. In order to realize such a quantum simulator, the necessary experimental foundation must rst be developed. Here experimental eorts were focused on addressing two primary issues: 1) designing and fabricating low disorder lattices that are readily available to incorporate superconducting qubits, and 2) developing new measurement tools and techniques that can be used to characterize large lattices, and probe the predicted quantum phases within the lattice. Three experiments addressing these issues were performed. In the rst experiment a Kagome lattice of transmission line resonators was designed and fabricated, and a comprehensive study on the eects of random disorder in the lattice demonstrated that disorder was dependent on the resonator geometry. Subsequently a cryogenic 3-axis scanning stage was developed and the operation of the scanning stage was demonstrated in the nal two experiments. The rst scanning experiment was conducted on a 49 site Kagome lattice, where a sapphire defect was used to locally perturb each lattice site. This perturbative scanning probe microscopy provided a means to measure the distribution of photon modes throughout the entire lattice. The second scanning experiment was performed on a single transmission line resonator where a transmon qubit was fabricated on a separate substrate, mounted to the tip of the scanning stage and coupled to the resonator. Here the coupling strength of the qubit to the resonator was mapped out demonstrating strong coupling over a wide scanning range, thus indicating the potential for a scanning qubit to be used as a local quantum probe.

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Last updated on 02/02/2021

Tunable coupling circuit quantum electrodynamics

Tunable coupling circuit quantum electrodynamics

Thesis Type:

PhD

Abstract:

Superconducting circuits have shown promise for exploring quantum optics and computing. This thesis presents an additional element, the tunable coupling qubit (TCQ), to the toolbox available for exploring such physics. The TCQ is shown to have independently tunable qubit energy and dipole coupling strength. High frequency flux control lines allow the varying of the TCQ's properties on very fast time scales. This enables qubit coherence measurements and the calculation of a lower bound on the maximum range of coupling strength tunability. Finally, an experiment demonstrating the TCQ's applicability in quantum state transfer is discussed.

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Last updated on 02/02/2021

Reservoir engineering in circuit quantum electrodynamics

Reservoir engineering in circuit quantum electrodynamics

Thesis Type:

PhD

Abstract:

Superconducting circuits have become an ideal platform to implement prototypi- cal quantum computing ideas and to study nonequilibrium quantum dynamics. This thesis covers research topics conducted in both subfields. Fast and reliable readout of volatile quantum states is one of the key requirements to build a universal quantum computer. In the first part, we utilize a number of techniques, ranging from a low noise amplifier to an on-chip stepped-impedance Purcell filter, to improve superconducting qubits readout fidelity. Interestingly, full quantum theory of SIPF requires the understanding of strong coupling quantum electrodynamics near a photonic band-gap. This problem, intimately tied to quantum impurity problems in condensed matter physics, has never been studied experimentally prior to the development of superconducting circuits. This realization then leads to the second part, the study of atom-light interaction in structured vacuum. The word ‘structured’ means the spectral function of the vacuum is drastically different from that of free space. We directly couple a transmon qubit to a microwave photonic crystal and discuss the concepts of photon bound states and quantum dissipative engineering in such a system. Following this research direction, quantum electrodynamics in a driven multimode cavity, another form of structured vacuum, is also investigated both experimentally and theoretically. The most intriguing phenomenon is the multimode ultranarrow resonance fluorescence, attributed to correlated light emission.

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Last updated on 02/02/2021