15 research outputs found
Entanglement in a quantum annealing processor
Entanglement lies at the core of quantum algorithms designed to solve
problems that are intractable by classical approaches. One such algorithm,
quantum annealing (QA), provides a promising path to a practical quantum
processor. We have built a series of scalable QA processors consisting of
networks of manufactured interacting spins (qubits). Here, we use qubit
tunneling spectroscopy to measure the energy eigenspectrum of two- and
eight-qubit systems within one such processor, demonstrating quantum coherence
in these systems. We present experimental evidence that, during a critical
portion of QA, the qubits become entangled and that entanglement persists even
as these systems reach equilibrium with a thermal environment. Our results
provide an encouraging sign that QA is a viable technology for large-scale
quantum computing.Comment: 13 pages, 8 figures, contact corresponding author for Supplementary
Informatio
Experimental Demonstration of a Robust and Scalable Flux Qubit
This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevB.81.134510.A rf–superconducting quantum interference device (SQUID) flux qubit that is robust against fabrication variations in Josephson-junction critical currents and device inductance has been implemented. Measurements of the persistent current and of the tunneling energy between the two lowest-lying states, both in the coherent and incoherent regimes, are presented. These experimental results are shown to be in agreement with predictions of a quantum-mechanical Hamiltonian whose parameters were independently calibrated, thus justifying the identification of this device as a flux qubit. In addition, measurements of the flux and critical current noise spectral densities are presented that indicate that these devices with Nb wiring are comparable to the best Al wiring rf SQUIDs reported in the literature thus far, with a 1/f flux noise spectral density at 1 Hz of 1.3+0.7−0.5 μΦ0/Hz−−√. An explicit formula for converting the observed flux noise spectral density into a free-induction-decay time for a flux qubit biased to its optimal point and operated in the energy eigenbasis is presented
Experimental Demonstration of a Robust and Scalable Flux Qubit
A novel rf-SQUID flux qubit that is robust against fabrication variations in
Josephson junction critical currents and device inductance has been
implemented. Measurements of the persistent current and of the tunneling energy
between the two lowest lying states, both in the coherent and incoherent
regime, are presented. These experimental results are shown to be in agreement
with predictions of a quantum mechanical Hamiltonian whose parameters were
independently calibrated, thus justifying the identification of this device as
a flux qubit. In addition, measurements of the flux and critical current noise
spectral densities are presented that indicate that these devices with Nb
wiring are comparable to the best Al wiring rf-SQUIDs reported in the
literature thusfar, with a flux noise spectral density at Hz of
. An explicit formula for
converting the observed flux noise spectral density into a free induction decay
time for a flux qubit biased to its optimal point and operated in the energy
eigenbasis is presented.Comment: 20 pages, 16 figure