RESUMEN
We report a system where fixed interactions between noncomputational levels make bright the otherwise forbidden two-photon |00}â|11} transition. The system is formed by hand selection and assembly of two discrete component transmon-style superconducting qubits inside a rectangular microwave cavity. The application of a monochromatic drive tuned to this transition induces two-photon Rabi-like oscillations between the ground and doubly excited states via the Bell basis. The system therefore allows all-microwave two-qubit universal control with the same techniques and hardware required for single qubit control. We report Ramsey-like and spin echo sequences with the generated Bell states, and measure a two-qubit gate fidelity of F(g)=90% (unconstrained) and 86% (maximum likelihood estimator).
RESUMEN
We use quantum process tomography to characterize a full universal set of all-microwave gates on two superconducting single-frequency single-junction transmon qubits. All extracted gate fidelities, including those for Clifford group generators, single-qubit π/4 and π/8 rotations, and a two-qubit controlled-not, exceed 95% (98%), without (with) subtracting state preparation and measurement errors. Furthermore, we introduce a process map representation in the Pauli basis which is visually efficient and informative. This high-fidelity gate set serves as a critical building block towards scalable architectures of superconducting qubits for error correction schemes and pushes up on the known limits of quantum gate characterization.
RESUMEN
We demonstrate an all-microwave two-qubit gate on superconducting qubits which are fixed in frequency at optimal bias points. The gate requires no additional subcircuitry and is tunable via the amplitude of microwave irradiation on one qubit at the transition frequency of the other. We use the gate to generate entangled states with a maximal extracted concurrence of 0.88, and quantum process tomography reveals a gate fidelity of 81%.
RESUMEN
We report quantum coherence measurements of a superconducting qubit whose design is a hybrid of several existing types. Excellent coherence times are found: T2â¼T1â¼1.5 µs. The topology of the qubit is that of a traditional three-junction flux qubit, but it has a large shunting capacitance, and the ratio of the junction critical currents is chosen so that the qubit potential has a single-well form. The qubit has a sizable nonlinearity, but its sign is reversed compared with most other popular qubit designs. The qubit is read out dispersively using a high-Q resonator in a λ/2 configuration.
RESUMEN
We have fabricated several 50 omega characteristic impedance low-pass metal powder filters. The filters are made with bronze or copper metal powder with varying amounts of metal powder in a metal powder/epoxy mixture. Our goal is to make a filter with a characteristic impedance Z = 50 omega at frequencies up to 10 GHz. Using a 78% bronze powder/epoxy mixture in a suitable geometry, we achieved an impedance Z = 54 omega at 4.2 K, with a cutoff frequency fc approximately/= 0.3 GHz and an attenuation A = Vout/Vin=0.0001 (-80 dB) at 10 GHz. We also made several non-50 omega low-pass bronze powder filters with fc = 1 MHz and A = 0.0001 at 10 MHz. Fabrication details and performance data will be presented for both types of filter.
RESUMEN
We experimentally demonstrate the use of a superconducting transmission line, shorted at both ends, to stabilize the operation of a tunable flux qubit. Using harmonic-oscillator stabilization and pulsed dc operation, we have observed Larmor oscillations with a single shot visibility of 90%. In another qubit, the visibility was 60% and there was no measurable visibility reduction after 35 ns.