I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
28
Okt
2016
Observation of the Bloch-Siegert shift in the driven quantum-to-classical transition of a dispersive transmon qubit
We demonstrate the Bloch-Siegert effect in a dispersively coupled qubit-cavity system which is driven through a quantum-to-classical transition. The observed dispersive shift of the
resonance frequency displays strongly non-monotonic dependence on the number of cavity photons and escapes the scope of the analytic results obtained with either a simple rotating-wave approximation, or with a more refined counter-rotating hybridized rotating wave approach. We measured the transition energy with a weak resonant probe, and the obtained data is in a good agreement with our numerical simulations of the quasienergy spectrum.
27
Okt
2016
Implementation of traveling odd Schrödinger cat states in circuit-QED
We propose a realistic scheme of generating a traveling odd Schr$“o$dinger cat state and a generalized entangled coherent state in circuit quantum electrodynamics (circuit-QED).
A squeezed vacuum state is used as initial resource of nonclassical states, which can be created through a Josephson traveling-wave parametric amplifier, and travels through a transmission line. Because a single-photon subtraction from the squeezed vacuum gives with very high fidelity an odd Schr$\“o$dinger cat state, we consider a specific circuit-QED setup consisting of the Josephson amplifier creating the traveling resource in a line, a beam-splitter coupling two transmission lines, and a single photon detector located at the end of the other line. When a single microwave photon is detected by measuring the excited state of a superconducting qubit in the detector, a heralded cat state is generated with high fidelity in the opposite line. For example, we show that the high fidelity of the outcome with the ideal cat state can be achieved with appropriate squeezing parameters theoretically. As its extended setup, we suggest that generalized entangled coherent states can be also built probabilistically and useful for microwave quantum information processing for error-correctable qudits in circuit-QED.
26
Okt
2016
All silicon Josephson junctions
We have realised laser-doped all-silicon superconducting (S)/ normal metal (N) bilayers of tunable thickness and dopant concentration. We observed a strong reduction of the bilayers
critical temperature when increasing the normal metal thickness, a signature of the highly transparent S/N interface associated to the epitaxial sharp laser doping profile. We extracted the interface resistance by fitting with the linearised Usadel equations, demonstrating a reduction of one order of magnitude from previous superconductor/doped Si interfaces. In this well controlled crystalline system we exploited the low resistance S/N interfaces to elaborate all-silicon lateral SNS Josephson junctions with long range proximity effect. Their dc transport properties, such as the critical and retrapping currents, could be well understood in the diffusive regime. Furthermore, this work lead to the estimation of important parameters in ultra-doped superconducting Si, such as the Fermi velocity, the coherence length, or the electron-phonon coupling constant, fundamental to conceive an all-silicon superconducting electronics.
25
Okt
2016
Implementation of pairwise longitudinal coupling in a three-qubit superconducting circuit
We present the „trimon“, a multi-mode superconducting circuit implementing three qubits with all-to-all longitudinal coupling. This always-on interaction enables simple
implementation of generalized controlled-NOT gates which form a universal set. Further, two of the three qubits are protected against Purcell decay while retaining measurability. We demonstrate high-fidelity state swapping operations between two qubits and characterize the coupling of all three qubits to a neighbouring transmon qubit. Our results offer a new paradigm for multi-qubit architecture with applications in quantum error correction, quantum simulations and quantum annealing.
Dynamical Casimir Effect for Gaussian Boson Sampling
We show that the Dynamical Casimir Effect (DCE), realized on two multimode coplanar waveguide resonators, implements a gaussian boson sampler (GBS). The appropriate choice of the mirror
acceleration that couples both resonators translates into the desired initial gaussian state and many-boson interference in a boson sampling network. In particular, we show that the proposed quantum simulator naturally performs a classically hard task, known as scattershot boson sampling. Our result unveils an unprecedented computational power of DCE, and paves the way for using DCE as a resource for quantum simulation.
Josephson junction microwave modulators for qubit control
We demonstrate Josephson junction based double-balanced mixer and phase shifter circuits operating at 6-10 GHz, and integrate these components to implement both a monolithic amplitude/phase
vector modulator and a quadrature mixer. The devices are actuated by flux signals, dissipate no power on chip, exhibit input saturation powers in excess of 1 nW, and provide cryogenic microwave modulation solutions for integrated control of superconducting qubits.
24
Okt
2016
Mesoscopic fluctuations in biharmonically driven flux qubits
We investigate flux qubits driven by a biharmonic magnetic signal, with a phase lag that acts as an effective time reversal broken parameter. The driving induced transition rate between
the ground and the excited state of the flux qubit can be thought as an effective transmitance, profiting from a direct analogy between interference effects at avoided level crossings and scattering events in disordered electronic systems. For time scales prior to full relaxation but large compared to the decoherence time, this characteristic rate has been accessed experimentally and its sensitivity with both the phase lag and the dc flux detuning explored. In this way signatures of Universal Conductance Fluctuations-like effects have recently been analized in flux qubits and compared with a phenomenological model that only accounts for decoherence, as a classical noise. We here solve the full dynamics of the driven flux qubit in contact with a quantum bath employing the Floquet Markov Master equation. Within this formalism relaxation and decoherence rates result strongly dependent on both the phase lag and the dc flux detuning. Consequently, the associated pattern of fluctuations in the characteristic rates display important differences with those obtained within the mentioned phenomenological model. In particular we demonstrate the Weak Localization-like effect in the averages values of the relaxation rate. Our predictions can be tested for accessible, but longer time scales than the current experimental times.
20
Okt
2016
Robust quantum state transfer between two superconducting qubits via partial measurement
We develop a potentially practical proposal for robust quantum state transfer (QST) between two superconducting qubits coupled by a coplanar waveguide (CPW) resonator. We show that
the partial measurement could drastically enhance the fidelity even when the dissipation of qubits and CPW is considered. Unlike many other schemes for QST, our proposal does not require the couplings between the qubits and the CPW resonator to be strong. In fact, our method works much more efficiently in the weak coupling regime. The underlying mechanism is attributed to the probabilistic nature of partial measurement.
19
Okt
2016
Transferring arbitrary d-dimensional quantum states of a superconducting qudit in circuit QED
A qudit (d-level quantum systems) has a large Hilbert space and thus can be used to achieve many quantum information and communication tasks. Here, we propose a method to transfer arbitrary
d-dimensional quantum states (known or unknown) between two superconducting qudits coupled to a single cavity. The state transfer can be performed fast because of employing resonant interactions only. In addition, quantum states can be deterministically transferred without measurement. Numerical simulations show that high-fidelity transfer of quantum states between two superconducting transmon qudits (d≤5) is feasible with current circuit QED technology. This proposal is quite general and can be applied to accomplish the same task with various superconducting qudits, quantum dots, or natural atoms coupled to a cavity or resonator.
18
Okt
2016
Circuit Quantum Electrodynamics Architecture for Gate-Defined Quantum Dots in Silicon
We demonstrate a hybrid device architecture where the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave
cavity. A quality factor Q = 5,400 is achieved by selectively etching away regions of the quantum well and by reducing photon losses through low-pass filtering of the gate bias lines. Homodyne measurements of the cavity transmission reveal DQD charge stability diagrams. These measurements indicate that electrons trapped in a Si DQD can be effectively coupled to microwave photons, potentially enabling coherent electron-photon interactions in silicon.