Consistency of Ground State and Spectroscopic Measurements on Flux Qubits

Abstract

We compare the results of ground state and spectroscopic measurements carried out on superconducting flux qubits which are effective two-level quantum systems. For a single qubit and for two coupled qubits we show excellent agreement between the parameters of the pseudospin Hamiltonian found using both methods. We argue that by making use of the ground state measurements the Hamiltonian of N coupled flux qubits can be reconstructed as well at temperatures smaller than the energy level separation. Such a reconstruction of a many-qubit Hamiltonian can be useful for future quantum information processing devices.

Stark Effect and Generalized Bloch-Siegert Shift in a Strongly Driven Two-Level System

“…We refer to these additional changes in the qubit level splitting as the generalized Bloch-Siegert shift. This work differs from the previous studies on strong drive with superconducting or quantum dot qubits [5,6,[15][16][17][18][19][20][21][22][23][24][25][26], where the coupling of the drive to the qubit was linear.…”

Experimental demonstration of a robust and scalable flux qubit

“…For those whose interests lie in developing hardware for AQO or forms of GMQC that likewise encode the logical basis into the flux basis, it is far more convenient to have a set of tools for characterizing quantum-mechanical properties that require only low bandwidth bias controls. Such methods, some appropriate in the coherent regime 51,52 and others in the incoherent regime, 36,47,53 have been reported in the literature. We have made use of such low-frequency methods as our apparatuses typically possess 128 low bandwidth bias lines to facilitate the adiabatic manipulation of a large number of devices.…”

“…51 An unfortunate consequence of the choice of design parameters for our highfidelity QFP-enabled readout scheme is that the QFP is relatively strongly coupled to the qubit, thus limiting its utility as a detector when the qubit tunnel barrier is suppressed. One can circumvent this problem within our device architecture by tuning an interqubit coupler to a finite mutual inductance and using a second qubit as a latching sensor, in much the same manner as a QFP.…”

Coherent manipulation of single electron spins with Landau-Zener sweeps

“…It has found applications modeling nano-electro-mechanical systems [12], opto-mechanical systems [13], Bose liquids [14], molecular magnets [15], Rydberg atoms [16], superconducting qubits [12,[17][18][19][20] and semiconductor singlet-triplet qubits [21][22][23]. In the LZSM model the energy difference between two coupled states is varied linearly in time, while the coupling between the states is time independent.…”

“…This method is convenient due to the fact that manipulation can be done electrically, without the precise knowledge of the spin resonance condition, and is robust against Zeeman level broadening caused by nuclear spins. [12,[17][18][19][20] and semiconductor singlet-triplet qubits [21][22][23]. In the LZSM model the energy difference between two coupled states is varied linearly in time, while the coupling between the states is time independent.…”