dc measurements of macroscopic quantum levels in a superconducting qubit structure with a time-ordered meter

Crankshaw, D.S.; Segall, K.; Nakada, D.; Orlando, Terry P.; Levitov, L. S.; Lloyd, Seth; Valenzuela, Sergio O.; Marković, Nina; Tinkham, M.; Berggren, Karl K.

doi:10.1103/physrevb.69.144518

Cited by 11 publications

(11 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From , we can determine the quality factor of classical small oscillation in the potential well . These results are consistent with our previous intra-well energy relaxation time measurements as well as dc spectroscopy measurements [15], [17], [18].…”

Section: Experiments and Resultssupporting

confidence: 93%

Energy Relaxation Times in a Nb Persistent Current Qubit

Oliver

Nakada

et al. 2005

IEEE Trans. Appl. Supercond.

Self Cite

View full text Add to dashboard Cite

show abstract

Section: Experiments and Resultssupporting

confidence: 93%

Energy Relaxation Times in a Nb Persistent Current Qubit

Oliver

Nakada

et al. 2005

IEEE Trans. Appl. Supercond.

Self Cite

View full text Add to dashboard Cite

show abstract

“…HOMRT has been observed in many different rf SQUIDs and is a well-established quantummechanical phenomenon. 36,49,50 LOMRT proved to be more difficult to observe in practice and was only reported upon relatively recently in the literature. 47 We refer the reader to this latter reference for the experimental method for measuring MRT rates.…”

Section: Rf-squid Capacitancementioning

confidence: 99%

Experimental demonstration of a robust and scalable flux qubit

et al. 2010

View full text Add to dashboard Cite

A rf-superconducting quantum interference device ͑SQUID͒ 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 −0.5 +0.7 ⌽ 0 / ͱ Hz. An explicit formula for converting the observed flux noise spectral density into a freeinduction-decay time for a flux qubit biased to its optimal point and operated in the energy eigenbasis is presented. I. MOTIVATIONExperimental efforts to develop useful solid-state quantum information processors have encountered a host of practical problems that have substantially limited progress. While the desire to reduce noise in solid-state qubits appears to be the key factor that drives much of the recent work in this field, it must be acknowledged that there are formidable challenges related to architecture, circuit density, fabrication variation, calibration, and control that also deserve attention. For example, a qubit that is inherently exponentially sensitive to fabrication variations with no recourse for in situ correction holds little promise in any large-scale architecture, even with the best of modern fabrication facilities. Likewise, a qubit that requires an inordinate number of custom-tuned time-dependent control signals to be launched onto the chip, in order to correct for fabrication variations or to compensate for unintended on-chip crosstalk, would also not be useful in a large-scale processor. Thus, a qubit designed in the absence of information concerning its ultimate use in a larger-scale system may prove to be of little utility in the future. In what follows, we present an experimental demonstration of a superconducting flux qubit 1 that has been specifically designed to address several issues that pertain to the implementation of a large-scale quantum information processor. While noise is not the central focus of this paper, we nonetheless present experimental evidence that, despite its physical size and relative complexity, the observed flux noise in this flux qubit is comparable to the quietest such devices reported on in the literature to date.It has been well established that rf superconducting quantum interference devices ͑SQUIDs͒ can be used as qubits given an appropriate choice of device parameters. Such devices can be operated as a flux-biased phase qubit using two intrawell energy levels 2 or as a flux qubit using...

show abstract

“…Superconducting circuits have played an essential role in realizing quantum mechanical phenomena in macroscopic systems. One such example is the observation of macroscopic resonant tunneling (MRT) of magnetic flux between the lowest energy states of single rf-SQUID flux qubits, as demonstrated by several groups [1][2][3][4]. These measurements provide both a clear signature of quantum mechanics in a macroscopic circuit at a finite temperature and in the presence of noise and a direct means of determining the tunneling energy between states.…”

mentioning

confidence: 99%

Cotunneling in pairs of coupled flux qubits

et al. 2010

View full text Add to dashboard Cite

We report measurements of macroscopic resonant tunneling between the two lowest energy states of a pair of magnetically coupled rf-SQUID flux qubits. This technique provides a direct means of observing two-qubit dynamics and a probe of the environment coupled to the pair of qubits. Measurements of the tunneling rate as a function of qubit flux bias show a Gaussian line shape that is well matched to theoretical predictions. Moreover, the peak widths indicate that each qubit is coupled to a local environment whose fluctuations are uncorrelated with that of the other qubit.Superconducting circuits have played an essential role in realizing quantum mechanical phenomena in macroscopic systems. One such example is the observation of macroscopic resonant tunneling (MRT) of magnetic flux between the lowest energy states of single rf-SQUID flux qubits, as demonstrated by several groups [1][2][3][4]. These measurements provide both a clear signature of quantum mechanics in a macroscopic circuit at a finite temperature and in the presence of noise and a direct means of determining the tunneling energy between states. Theoretical descriptions of the MRT rate have been presented [5,6] and indicate a direct connection between the profile of the MRT rate peaks and properties of the environment. Analogous measurements of the tunneling of magnetization in nanomagnets [7,8] suggest that MRT is responsible for dynamics in these materials as well.In this work, we extend measurements of MRT to inductively coupled pairs of flux qubits. We present experimental observations of tunneling between the two lowest energy states of the coupled system for several coupling strengths. These data yield two-qubit energy gaps that match those predicted by the independently calibrated Hamiltonian of the coupled system. Moreover, measurements of the two-qubit energy gap are used to infer single qubit energy gaps at ∼ h × 10 9 Hz without the use of microwave lines. Finally, the profile of the MRT rate versus qubit flux bias has a Gaussian lineshape with a width that is a factor of √ 2 larger than that of a single qubit. We argue that this observation indicates that the environments coupled to each qubit are uncorrelated.For a single flux qubit, an MRT experiment consists of measuring the rate of tunneling of flux between two wells of the double-well potential of the rf SQUID when the lowest energy levels of each well are closely aligned. Restricting the dynamics of the single rf SQUID to its two lowest energy states allows one to map the physics of this device onto the canonical qubit Hamiltonian:where σ x,z are Pauli matrices, ǫ ≡ 2I p (Φ (1) is valid when |ǫ|, ∆ ≪hω p , wherehω p is the energy spacing to the next excited state of the rf SQUID. For a non-Markovian environment [9], the initial tunneling rate from |0 to |1 (eigenstates of σ z ) versus ǫ has a Gaussian profile, as given by Eq. (2) in Ref. [2].A natural extension to the single qubit MRT experiment is to add a second qubit that is inductively coupled to a first qubit via a mutual induct...

show abstract

dc measurements of macroscopic quantum levels in a superconducting qubit structure with a time-ordered meter

Cited by 11 publications

References 19 publications

Energy Relaxation Times in a Nb Persistent Current Qubit

Energy Relaxation Times in a Nb Persistent Current Qubit

Experimental demonstration of a robust and scalable flux qubit

Cotunneling in pairs of coupled flux qubits

Contact Info

Product

Resources

About