High coherence hybrid superconducting qubit

We measure the coherence of a new superconducting qubit, the {\em low-impedance flux qubit}, finding $T_2^* \sim T_1 \sim 1.5\mu$s. It is a three-junction flux qubit, but the ratio of junction critical currents is chosen to make the qubit's potential have a single well form. The low impedance of its large shunting capacitance protects it from decoherence. This qubit has a moderate anharmonicity, whose sign is reversed compared with all other popular qubit designs. The qubit is capacitively coupled to a high-Q resonator in a $\lambda/2$ configuration, which permits the qubit's state to be read out dispersively

Killer whale population in decline : how is the decreasing population of Southern Resident killer whales connected to prey selection and availability?

Overview: The population of Southern Resident killer whales has been on the decline for decades, dropping 20% since the mid 1990s. Starvation appears to be a factor in the deaths of many of these whales. The Southern Resident killer whales survive mainly on a diet of Chinook salmon, which is another species in decline due to a variety of human impacts. In this lesson, students explore how the selective feeding practices of Southern Resident killer whales contribute to their declining numbers.Learning Goals: Students will learn the following: • Southern Resident killer whale (SRKW) and Chinook salmon populations are in significant decline due to the impacts of human activities on marine ecosystems. • Environmental changes affect food web dynamics. • SRKWs and juvenile Chinook salmon are selective feeders. • Effective species recovery plans for SRKW and Chinook salmon include an understanding of ecosystem relationships

A simple all-microwave entangling gate for fixed-frequency superconducting qubits

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%

Decoherence of floating qubits due to capacitive coupling

It has often been assumed that electrically floating qubits, such as flux qubits, are immune to decoherence due to capacitive coupling. We show that capacitive coupling to bias leads can be a dominant source of dissipation, and therefore of decoherence, for such floating qubits. Classical electrostatic arguments are sufficient to get a good estimate of this source of relaxation for standard superconducting qubit designs. We show that relaxation times can be improved by designing floating qubits so they couple symmetrically to the bias leads. Observed coherence times of flux qubits with varying degrees of symmetry qualitatively support our results.Comment: V1: 4 pages, 3 figures. V2: 5 pages, 3 figures. Published versio

Efficient measurement of quantum gate error by interleaved randomized benchmarking

We describe a scalable experimental protocol for obtaining estimates of the error rate of individual quantum computational gates. This protocol, in which random Clifford gates are interleaved between a gate of interest, provides a bounded estimate of the average error of the gate under test so long as the average variation of the noise affecting the full set of Clifford gates is small. This technique takes into account both state preparation and measurement errors and is scalable in the number of qubits. We apply this protocol to a superconducting qubit system and find gate errors that compare favorably with the gate errors extracted via quantum process tomography.Comment: 5 pages, 2 figures, published versio