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Energy redistribution between quasiparticles in mesoscopic silver wiresDec 08 1999We have measured with a tunnel probe the energy distribution function of quasiparticles in silver diffusive wires connected to two large pads (``reservoirs''), between which a bias voltage was applied. From the dependence in energy and bias voltage of ... More

Two-mode Correlation of Microwave Quantum Noise Generated by Parametric Down-ConversionNov 17 2010In this letter, we report the observation of the correlation between two modes of microwave radiation resulting from the amplification of quantum noise by the Josephson Parametric Converter. This process, seen from the pump, can be viewed as parametric ... More

Planar Superconducting Whispering Gallery Mode ResonatorsAug 08 2013Oct 07 2013We introduce a microwave circuit architecture for quantum signal processing combining design principles borrowed from high-Q 3D resonators in the quantum regime and from planar structures fabricated with standard lithography. The resulting '2.5D' whispering-gallery ... More

Charging effects in the inductively shunted Josephson junctionFeb 17 2009Oct 20 2009The choice of impedance used to shunt a Josephson junction determines if the charge transferred through the circuit is quantized: a capacitive shunt renders the charge discrete, whereas an inductive shunt leads to continuous charge. This discrepancy leads ... More

Introduction to Quantum Electromagnetic CircuitsOct 11 2016The article is a short opinionated review of the quantum treatment of electromagnetic circuits, with no pretension to exhaustiveness. This review, which is an updated and modernized version of a previous set of Les Houches School lecture notes, has 3 ... More

Introduction to Quantum Electromagnetic CircuitsOct 11 2016Jun 09 2017The article is a short opinionated review of the quantum treatment of electromagnetic circuits, with no pretension to exhaustiveness. This review, which is an updated and modernized version of a previous set of Les Houches School lecture notes, has 3 ... More

Conductance Fluctuations in a Metallic Wire Interrupted by a Tunnel JunctionApr 14 1997The conductance fluctuations of a metallic wire which is interrupted by a small tunnel junction has been explored experimentally. In this system, the bias voltage V, which drops almost completely inside the tunnel barrier, is used to probe the energy ... More

Stabilizing a Bell state of two superconducting qubits by dissipation engineeringMar 15 2013We propose a dissipation engineering scheme that prepares and protects a maximally entangled state of a pair of superconducting qubits. This is done by off-resonantly coupling the two qubits to a low-Q cavity mode playing the role of a dissipative reservoir. ... More

Probing interactions in mesoscopic gold wiresDec 04 2000We have measured in gold wires the energy exchange rate between quasiparticles, the phase coherence time of quasiparticles and the resistance vs. temperature, in order to probe the interaction processes which are relevant at low temperatures. We find ... More

Nonequilibrium quasiparticles and $2e$ periodicity in single-Cooper-pair transistorsAug 13 2003We have fabricated single-Cooper-pair transistors in which the spatial profile of the superconducting gap energy was controlled by oxygen doping. The profile dramatically affects the switching current \textit{vs.} gate voltage curve of the transistor, ... More

Dispersive measurements of superconducting qubit coherence with a fast, latching readoutJul 25 2005Sep 07 2005The "quantronium" is a superconducting qubit consisting of a split Cooper pair box in which a large tunnel junction is inserted. This circuit has a special bias point where the Larmor frequency is, to first order, insensitive to fluctuations in the bias ... More

RF bifurcation of a Josephson junction: microwave embedding circuit requirementsDec 22 2006A Josephson tunnel junction which is RF-driven near a dynamical bifurcation point can amplify quantum signals. The bifurcation point will exist robustly only if the electrodynamic environment of the junction meets certain criteria. In this article we ... More

Influence of Magnetic Field on Effective Electron-Electron Interactions in a Copper WireSep 17 2001We have measured in a copper wire the energy exchange rate between quasiparticles as a function of the applied magnetic field. We find that the effective electron-electron interaction is strongly modified by the magnetic field, suggesting that magnetic ... More

Theory of remote entanglement via quantum-limited phase-preserving amplificationJul 02 2015Jun 07 2016We show that a quantum-limited phase-preserving amplifier can act as a which-path information eraser when followed by heterodyne detection. This 'beam splitter with gain' implements a continuous joint measurement on the signal sources. As an application, ... More

Improving the Quality Factor of Microwave Compact Resonators by Optimizing their Geometrical ParametersApr 03 2012Jun 05 2012Applications in quantum information processing and photon detectors are stimulating a race to produce the highest possible quality factor on-chip superconducting microwave resonators. We have tested the surface-dominated loss hypothesis by systematically ... More

Evidence for saturation of channel transmission from conductance fluctuations in atomic-size point contactsOct 28 1998Jul 19 1999The conductance of atomic size contacts has a small, random, voltage dependent component analogous to conductance fluctuations observed in diffusive wires (UCF). A new effect is observed in gold contacts, consisting of a marked suppression of these fluctuations ... More

Life after charge noise: recent results with transmon qubitsDec 10 2008We 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 ... More

Relaxation and frequency shifts induced by quasiparticles in superconducting qubitsJun 04 2011As low-loss non-linear elements, Josephson junctions are the building blocks of superconducting qubits. The interaction of the qubit degree of freedom with the quasiparticles tunneling through the junction represent an intrinsic relaxation mechanism. ... More

Quasiparticle relaxation of superconducting qubits in the presence of fluxJan 07 2011Jan 21 2011Quasiparticle tunneling across a Josephson junction sets a limit for the lifetime of a superconducting qubit state. We develop a general theory of the corresponding decay rate in a qubit controlled by a magnetic flux. The flux affects quasiparticles tunneling ... More

Multilayer microwave integrated quantum circuits for scalable quantum computingSep 03 2015Sep 11 2015As experimental quantum information processing (QIP) rapidly advances, an emerging challenge is to design a scalable architecture that combines various quantum elements into a complex device without compromising their performance. In particular, superconducting ... More

Qubits as Spectrometers of Quantum NoiseOct 10 2002Electrical engineers and physicists are naturally very interested in noise in circuits, amplifiers and detectors. With the advent of quantum computation and other high frequency electronics operating at low temperatures, we have entered a regime where ... More

Introduction to Quantum Noise, Measurement and AmplificationOct 26 2008Apr 15 2010The topic of quantum noise has become extremely timely due to the rise of quantum information physics and the resulting interchange of ideas between the condensed matter and AMO/quantum optics communities. This review gives a pedagogical introduction ... More

3-Wave Mixing Josephson Dipole ElementFeb 02 2017Jun 01 2017Parametric conversion and amplification based on three-wave mixing are powerful primitives for efficient quantum operations. For superconducting qubits, such operations can be realized with a quadrupole Josephson junction element, the Josephson Ring Modulator ... More

Photon-assisted charge-parity jumps in a superconducting qubitApr 12 2019We evaluate the rates of energy and phase relaxation of a superconducting qubit caused by stray photons with energy exceeding the threshold for breaking a Cooper pair. All channels of relaxation within this mechanism are associated with the change in ... More

Optimizing the nonlinearity and dissipation of a SNAIL Parametric Amplifier for dynamic rangeJun 15 2018Dec 20 2018We present a new quantum-limited Josephson-junction-based 3-wave-mixing parametric amplifier, the SNAIL Parametric Amplifier (SPA), which uses an array of SNAILs (Superconducting Nonlinear Asymmetric Inductive eLements) as the source of tunable nonlinearity. ... More

Implementation of low-loss superinductances for quantum circuitsJun 13 2012The simultaneous suppression of charge fluctuations and offsets is crucial for preserving quantum coherence in devices exploiting large quantum fluctuations of the superconducting phase. This requires an environment with both extremely low DC and high ... More

Quantum versus classical switching dynamics of driven-dissipative Kerr resonatorsJun 24 2019We report a first-principles study of the driven-dissipative dynamics for Kerr oscillators in the mesoscopic regime. This regime is characterized by large Kerr nonlinearity, realized here using the nonlinear kinetic inductance of a large array of Josephson ... More

Kerr-free three-wave mixing in superconducting quantum circuitsFeb 27 2019Quantum-limited Josephson parametric amplifiers are crucial components in circuit QED readout chains. The dynamic range of state-of-the-art parametric amplifiers is limited by signal-induced Stark shifts that detune the amplifier from its operating point. ... More

Superconducting circuit protected by two-Cooper-pair tunnelingMay 03 2019We present a protected superconducting qubit based on an effective circuit element that only allows pairs of Cooper pairs to tunnel. These dynamics give rise to a nearly degenerate ground state manifold indexed by the parity of tunneled Cooper pairs. ... More

The reconfigurable Josephson circulator/directional amplifierMar 01 2015Oct 27 2015Circulators and directional amplifiers are crucial non-reciprocal signal routing and processing components involved in microwave readout chains for a variety of applications. They are particularly important in the field of superconducting quantum information, ... More

The Josephson Bifurcation Amplifier for Quantum MeasurementsJul 11 2005We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. ... More

An RF-Driven Josephson Bifurcation Amplifier for Quantum MeasurementsDec 24 2003We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. ... More

Simultaneous monitoring of fluxonium qubits in a waveguideMay 16 2017Sep 17 2017Most quantum-error correcting codes assume that the decoherence of each physical qubit is independent of the decoherence of any other physical qubit. We can test the validity of this assumption in an experimental setup where a microwave feedline couples ... More

Rabi oscillations, Ramsey fringes and spin echoes in an electrical circuitSep 13 2002We present a superconducting tunnel junction circuit which behaves as a controllable atom, and whose ground and first excited state form an effective spin 1/2. By applying microwave pulses, we have performed on this circuit experiments demonstrating the ... More

Direct Dispersive Monitoring of Charge Parity in Offset-Charge-Sensitive TransmonsMar 01 2019A striking characteristic of superconducting circuits is that their eigenspectra and intermode coupling strengths are well predicted by simple Hamiltonians representing combinations of quantum circuit elements. Of particular interest is the Cooper-pair-box ... More

Quantization of inductively-shunted superconducting circuitsFeb 04 2016Oct 20 2016We present a method for calculating the energy levels of superconducting circuits that contain highly anharmonic, inductively-shunted modes with arbitrarily strong coupling. Our method starts by calculating the normal modes of the linearized circuit and ... More

Non-degenerate, three-wave mixing with the Josephson ring modulatorAug 15 2012The Josephson ring modulator (JRM) is a device, based on Josephson tunnel junctions, capable of performing non-degenerate mixing in the microwave regime without losses. The generic scattering matrix of the device is calculated by solving coupled quantum ... More

Wireless Josephson AmplifierApr 19 2014Jul 21 2014Josephson junction parametric amplifiers are playing a crucial role in the readout chain in superconducting quantum information experiments. However, their integration with current 3D cavity implementations poses the problem of transitioning between waveguide, ... More

Demonstrating a Driven Reset Protocol of a Superconducting QubitNov 02 2012Mar 25 2013Qubit reset is crucial at the start of and during quantum information algorithms. We present the experimental demonstration of a practical method to force qubits into their ground state, based on driving certain qubit and cavity transitions. Our protocol, ... More

Manipulating the Quantum State of an Electrical CircuitMay 16 2002May 29 2002We have designed and operated a superconducting tunnel junction circuit that behaves as a two-level atom: the ``quantronium''. An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses, and a projective measurement ... More

Quantization of inductively-shunted superconducting circuitsFeb 04 2016Aug 19 2016We present a method for calculating the energy levels of superconducting circuits that contain highly anharmonic, inductively-shunted modes with arbitrarily strong coupling. Our method starts by calculating the normal modes of the linearized circuit and ... More

Quantum information processing with circuit quantum electrodynamicsDec 01 2006Jun 01 2007We theoretically study single and two-qubit dynamics in the circuit QED architecture. We focus on the current experimental design [Wallraff et al., Nature 431, 162 (2004); Schuster et al., Nature 445, 515 (2007)] in which superconducting charge qubits ... More

Analog information processing at the quantum limit with a Josephson ring modulatorMay 22 2008Oct 22 2009Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, they always degrade the information by adding noise. Quantum mechanics puts a limit on how small this degradation can be. Theoretically, the minimum noise energy ... More

Demonstration of superconducting micromachined cavitiesSep 03 2015Sep 11 2015Superconducting enclosures will be key components of scalable quantum computing devices based on circuit quantum electrodynamics (cQED). Within a densely integrated device, they can protect qubits from noise and serve as quantum memory units. Whether ... More

Quantum Channel Construction with Circuit Quantum ElectrodynamicsNov 10 2016Quantum channels can describe all transformations allowed by quantum mechanics. We provide an explicit universal protocol to construct all possible quantum channels, using a single qubit ancilla with quantum non-demolition readout and adaptive control. ... More

Conduction channels of superconducting quantum point contactsJan 25 2000Atomic quantum point contacts accommodate a small number of conduction channels. Their number N and transmission coefficients {T_n} can be determined by analyzing the subgap structure due to multiple Andreev reflections in the current-voltage (IV) characteristics ... More

Measuring the Decoherence of a Quantronium Qubit with the Cavity Bifurcation AmplifierJun 06 2007Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasiveness. We have developed such an amplifier, the Cavity Bifurcation Amplifier (CBA) [10], and applied it to the readout of the quantronium qubit [2]. It consists ... More

Preparation and Measurement of Three-Qubit Entanglement in a Superconducting CircuitApr 25 2010Traditionally, quantum entanglement has played a central role in foundational discussions of quantum mechanics. The measurement of correlations between entangled particles can exhibit results at odds with classical behavior. These discrepancies increase ... More

Stabilizing entanglement autonomously between two superconducting qubitsJul 16 2013Oct 23 2013Quantum error-correction codes would protect an arbitrary state of a multi-qubit register against decoherence-induced errors, but their implementation is an outstanding challenge for the development of large-scale quantum computers. A first step is to ... More

Quantum back-action of variable-strength measurementMar 27 2019Measuring a quantum system can randomly perturb its state. The strength and nature of this back-action depends on the quantity which is measured. In a partial measurement performed by an ideal apparatus, quantum physics predicts that the system remains ... More

A fluxonium-based artificial molecule with a tunable magnetic momentOct 04 2016Engineered quantum systems allow us to observe phenomena that are not easily accessible naturally. The LEGO-like nature of superconducting circuits makes them particularly suited for building and coupling artificial atoms. Here, we introduce an artificial ... More

Entanglement Metrology Using a Joint Readout of Superconducting QubitsAug 13 2009Accurate and precise detection of multi-qubit entanglement is key for the experimental development of quantum computation. Traditionally, non-classical correlations between entangled qubits are measured by counting coincidences between single-shot readouts ... More

Planar multilayer circuit quantum electrodynamicsSep 04 2015May 29 2016Experimental quantum information processing with superconducting circuits is rapidly advancing, driven by innovation in two classes of devices, one involving planar micro-fabricated (2D) resonators, and the other involving machined three-dimensional (3D) ... More

Phase preserving amplification near the quantum limit with a Josephson Ring ModulatorDec 17 2009Recent progress in solid state quantum information processing has stimulated the search for ultra-low-noise amplifiers and frequency converters in the microwave frequency range, which could attain the ultimate limit imposed by quantum mechanics. In this ... More

Driving forbidden transitions in the fluxonium artificial atomNov 20 2017May 31 2018Atomic systems display a rich variety of quantum dynamics due to the different possible symmetries obeyed by the atoms. These symmetries result in selection rules that have been essential for the quantum control of atomic systems. Superconducting artificial ... More

A fluxonium-based artificial molecule with a tunable magnetic momentOct 04 2016Dec 05 2016Engineered quantum systems allow us to observe phenomena that are not easily accessible naturally. The LEGO-like nature of superconducting circuits makes them particularly suited for building and coupling artificial atoms. Here, we introduce an artificial ... More

Sideband Transitions and Two-Tone Spectroscopy of a Superconducting Qubit Strongly Coupled to an On-Chip CavityMar 23 2007Sideband transitions are spectroscopically probed in a system consisting of a Cooper pair box strongly but non-resonantly coupled to a superconducting transmission line resonator. When the Cooper pair box is operated at the optimal charge bias point the ... More

Robust concurrent remote entanglement between two superconducting qubitsMar 11 2016Aug 08 2016Entangling two remote quantum systems which never interact directly is an essential primitive in quantum information science and forms the basis for the modular architecture of quantum computing. When protocols to generate these remote entangled pairs ... More

Hot non-equilibrium quasiparticles in transmon qubitsMar 01 2018Oct 14 2018Non-equilibrium quasiparticle excitations degrade the performance of a variety of superconducting circuits. Understanding the energy distribution of these quasiparticles will yield insight into their generation mechanisms, the limitations they impose ... More

General phase spaces: from discrete variables to rotor and continuum limitsSep 13 2017Oct 30 2017We provide a basic introduction to discrete-variable, rotor, and continuous-variable quantum phase spaces, explaining how the latter two can be understood as limiting cases of the first. We extend the limit-taking procedures used to travel between phase ... More

Direct microwave measurement of Andreev-bound-state dynamics in a proximitized semiconducting nanowireNov 05 2017The modern understanding of the Josephson effect in mesosopic devices derives from the physics of Andreev bound states, fermionic modes that are localized in a superconducting weak link. Recently, Josephson junctions constructed using semiconducting nanowires ... More

Degeneracy-preserving quantum non-demolition measurement of parity-type observables for cat-qubitsNov 03 2016A central requirement for any quantum error correction scheme is the ability to perform quantum non-demolition measurements of an error syndrome, corresponding to a special symmetry property of the encoding scheme. It is in particular important that such ... More

On-demand quantum state transfer and entanglement between remote microwave cavity memoriesDec 15 2017Modular quantum computing architectures require fast and efficient distribution of quantum information through propagating signals. Here we report rapid, on-demand quantum state transfer between two remote superconducting cavity quantum memories through ... More

Nonlinear response of the vacuum Rabi resonanceJul 17 2008On 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 ... More

Single-photon Resolved Cross-Kerr Interaction for Autonomous Stabilization of Photon-number StatesApr 13 2015Quantum states can be stabilized in the presence of intrinsic and environmental losses by either applying active feedback conditioned on an ancillary system or through reservoir engineering. Reservoir engineering maintains a desired quantum state through ... More

Direct Observation of Dynamical Switching between Two Driven Oscillation States of a Josephson JunctionDec 21 2003We performed a novel phase sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and non-linear regime. When the junction was driven below the plasma frequency into the non-linear ... More

Charge insensitive qubit design derived from the Cooper pair boxFeb 28 2007Sep 26 2007Short 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, ... More

Asymmetric frequency conversion in nonlinear systems driven by a biharmonic pumpMay 07 2014Dec 01 2014A novel mechanism of asymmetric frequency conversion is investigated in nonlinear dispersive devices driven parametrically with a biharmonic pump. When the relative phase between the first and second harmonics combined in a two-tone pump is appropriately ... More

Gated conditional displacement readout of superconducting qubitsSep 18 2018We have realized a new interaction between superconducting qubits and a readout cavity that results in the displacement of a coherent state in the cavity, conditioned on the state of the qubit. This conditional state, when it reaches the cavity-following, ... More

Inelastic Microwave Photon Scattering off a Quantum Impurity in a Josephson-Junction ArrayAug 01 2012Jan 09 2013Quantum fluctuations in an anharmonic superconducting circuit enable frequency conversion of individual incoming photons. This effect, linear in the photon beam intensity, leads to ramifications for the standard input-output circuit theory. We consider ... More

Deterministic remote entanglement of superconducting circuits through microwave two-photon transitionsDec 15 2017Large-scale quantum information processing networks will most probably require the entanglement of distant systems that do not interact directly. This can be done by performing entangling gates between standing information carriers, used as memories or ... More

A CNOT gate between multiphoton qubits encoded in two cavitiesSep 15 2017Dec 20 2017Entangling gates between qubits are a crucial component for performing algorithms in quantum computers. However, any quantum algorithm must ultimately operate on error-protected logical qubits encoded in high-dimensional systems. Typically, logical qubits ... More

Qubit-photon interactions in a cavity: Measurement induced dephasing and number splittingFeb 13 2006Aug 29 2006We theoretically study measurement induced-dephasing of a superconducting qubit in the circuit QED architecture and compare the results to those obtained experimentally by Schuster {\it et al.}, [Phys. Rev. Lett. 94, 123602 (2005)]. Strong coupling of ... More

Stabilized Cat in Driven Nonlinear Cavity: A Fault-Tolerant Error Syndrome DetectorJul 24 2018In quantum error correction, information is encoded in a high-dimensional system to protect it from the environment. A crucial step is to use natural, low-weight operations with an ancilla to extract information about errors without causing backaction ... More

Entangling Bosonic Modes via an Engineered Exchange InteractionJun 19 2018The realization of robust universal quantum computation with any platform ultimately requires both the coherent storage of quantum information and (at least) one entangling operation between individual elements. The use of continuous-variable bosonic ... More

Deterministic teleportation of a quantum gate between two logical qubitsJan 16 2018A quantum computer has the potential to effciently solve problems that are intractable for classical computers. Constructing a large-scale quantum processor, however, is challenging due to errors and noise inherent in real-world quantum systems. One approach ... More

Generating Single Microwave Photons in a CircuitFeb 27 2007Electromagnetic signals in circuits consist of discrete photons, though conventional voltage sources can only generate classical fields with a coherent superposition of many different photon numbers. While these classical signals can control and measure ... More

Suppressing Charge Noise Decoherence in Superconducting Charge QubitsDec 20 2007We 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., ... More

Coupling Superconducting Qubits via a Cavity BusSep 13 2007Superconducting 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 ... More

A Schrodinger Cat Living in Two BoxesJan 21 2016Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as "cat states", have been an elegant demonstration of Schrodinger's famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in ... More

Implementing and characterizing precise multi-qubit measurementsJun 02 2016Jun 07 2016There are two general requirements to harness the computational power of quantum mechanics: the ability to manipulate the evolution of an isolated system and the ability to faithfully extract information from it. Quantum error correction and simulation ... More

Observation of high coherence in Josephson junction qubits measured in a three-dimensional circuit QED architectureMay 23 2011Nov 02 2011Superconducting quantum circuits based on Josephson junctions have made rapid progress in demonstrating quantum behavior and scalability. However, the future prospects ultimately depend upon the intrinsic coherence of Josephson junctions, and whether ... More

Reaching 10 ms single photon lifetimes for superconducting aluminum cavitiesFeb 18 2013May 22 2013Three-dimensional microwave cavities have recently been combined with superconducting qubits in the circuit quantum electrodynamics (cQED) architecture. These cavities should have less sensitivity to dielectric and conductor losses at surfaces and interfaces, ... More

Tracking Photon Jumps with Repeated Quantum Non-Demolition Parity MeasurementsNov 11 2013Quantum error correction (QEC) is required for a practical quantum computer because of the fragile nature of quantum information. In QEC, information is redundantly stored in a large Hilbert space and one or more observables must be monitored to reveal ... More

Controlling the spontaneous emission of a superconducting transmon qubitMar 31 2008We 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 ... More

Coherent oscillations inside a quantum manifold stabilized by dissipationMay 05 2017Nov 13 2017Manipulating the state of a logical quantum bit usually comes at the expense of exposing it to decoherence. Fault-tolerant quantum computing tackles this problem by manipulating quantum information within a stable manifold of a larger Hilbert space, whose ... More

Experimental implementation of a Raman-assisted six-quanta processNov 15 2018Fault tolerant quantum information processing requires specific nonlinear interactions acting within the Hilbert space of the physical system that implements a logical qubit. The required order of nonlinearity is often not directly available in the natural ... More

Resolving photon number states in a superconducting circuitAug 30 2006Electromagnetic signals are always composed of photons, though 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 ... More

Confining the state of light to a quantum manifold by engineered two-photon lossDec 15 2014Physical systems usually exhibit quantum behavior, such as superpositions and entanglement, only when they are sufficiently decoupled from a lossy environment. Paradoxically, a specially engineered interaction with the environment can become a resource ... More

Measurements of Quasiparticle Tunneling Dynamics in a Bandgap-Engineered Transmon QubitDec 12 2011We have engineered the bandgap profile of transmon qubits by combining oxygen-doped Al for tunnel junction electrodes and clean Al as quasiparticle traps to investigate energy relaxation due to quasiparticle tunneling. The relaxation time $T_1$ of the ... More

Violating Bell's inequality with an artificial atom and a cat state in a cavityApr 09 2015The `Schr\"odinger's cat' thought experiment highlights the counterintuitive facet of quantum theory that entanglement can exist between microscopic and macroscopic systems, producing a superposition of distinguishable states like the fictitious cat that ... More

Non-Poissonian Quantum Jumps of a Fluxonium Qubit due to Quasiparticle ExcitationsJun 06 2014Dec 09 2014As the energy relaxation time of superconducting qubits steadily improves, non-equilibrium quasiparticle excitations above the superconducting gap emerge as an increasingly relevant limit for qubit coherence. We measure fluctuations in the number of quasiparticle ... More

Coherent oscillations between classically separable quantum states of a superconducting loopOct 16 2009Ten years ago, coherent oscillations between two quantum states of a superconducting circuit differing by the presence or absence of a single Cooper pair on a metallic island were observed for the first time. This result immediately stimulated the development ... More

Three-wave mixing with three incoming waves: Signal-Idler Coherent Cancellation and Gain Enhancement in a Parametric AmplifierJan 08 2013Coherent, purely-dispersive three-wave mixing systems in optics and superconducting microwave circuits can be operated as parametric amplifiers, generating from a pump wave at one frequency amplified signal and idler waves at lower frequencies. Here we ... More

Continuous quantum nondemolition measurement of the transverse component of a qubitMay 25 2016Sep 20 2016Quantum jumps of a qubit are usually observed between its energy eigenstates, also known as its longitudinal pseudo-spin component. Is it possible, instead, to observe quantum jumps between the transverse superpositions of these eigenstates? We answer ... More

Demonstrating Quantum Error Correction that Extends the Lifetime of Quantum InformationFeb 15 2016The remarkable discovery of Quantum Error Correction (QEC), which can overcome the errors experienced by a bit of quantum information (qubit), was a critical advance that gives hope for eventually realizing practical quantum computers. In principle, a ... More

Generating Entangled Microwave Radiation Over Two Transmission LinesApr 03 2012Oct 31 2012Using a superconducting circuit, the Josephson mixer, we demonstrate the first experimental realization of spatially separated two-mode squeezed states of microwave light. Driven by a pump tone, a first Josephson mixer generates, out of quantum vacuum, ... More

Structural instability of driven Josephson circuits prevented by an inductive shuntMay 19 2018Dec 12 2018Superconducting circuits are a versatile platform to implement a multitude of Hamiltonians which perform quantum computation, simulation and sensing tasks. A key ingredient for realizing a desired Hamiltonian is the irradiation of the circuit by a strong ... More

Measurement and Control of Quasiparticle Dynamics in a Superconducting QubitJun 27 2014Oct 24 2014Superconducting circuits have attracted growing interest in recent years as a promising candidate for fault-tolerant quantum information processing. Extensive efforts have always been taken to completely shield these circuits from external magnetic field ... More

Widely tunable, non-degenerate three-wave mixing microwave device operating near the quantum limitFeb 06 2012We present the first experimental realization of a widely frequency tunable, non-degenerate three-wave mixing device for quantum signals at GHz frequency. It is based on a new superconducting building-block consisting of a ring of four Josephson junctions ... More