Experiments on Superconducting Qubits Coupled to Resonators = Untersuchung an Resonatoren gekoppelter supraleitender Qubits

In the present thesis, a system to simultaneously measure many superconducting quantum bits using frequency-division multiplexing is developed. The theoretical and experimental foundations are introduced and parallel measurements on up to six qubits are demonstrated

3D microwave cavity with magnetic flux control and enhanced quality factor

Three-dimensional (3D) superconducting microwave cavities with large mode volumes typically have high quality factors ($>10^6$). This is due to a reduced sensitivity to surface dielectric losses, which is the limiting source of dissipation in two-dimensional transmission line resonators. In recent years, 3D microwave cavities have been extensively used for coupling and interacting with superconducting quantum bits (qubits), providing a versatile platform for quantum information processing and hybrid quantum systems. A current issue that has arisen is that 3D superconducting cavities do not permit magnetic field control of qubits embedded in these cavities. In contrast, microwave cavities made of normal metals can be transparent to magnetic fields, but experience a much lower quality factor ($\sim 10^4$), which negates many of the advantages of the 3D architecture. In an attempt to create a device that bridges a gap between these two types of cavities, having magnetic field control and high quality factor, we have created a hybrid 3D cavity. This new cavity is primarily composed of aluminium but also contains a small copper insert. We measured the internal quality factor of the hybrid cavity to be $102000$, which is an order of magnitude improvement over all previously tested copper cavities. An added benefit to that our hybrid cavity possesses is that it also provides an improved thermal link to the sample that superconducting cavities alone cannot provide. In order to demonstrate precise magnetic control within the cavity, we performed spectroscopy of three superconducting qubits placed in the cavity, where individual control of each qubit's frequency was exerted with small wire coils attached to the cavity. A large improvement in quality factor and magnetic field control makes this 3D hybrid cavity an attractive new platform for circuit quantum electrodynamics experiments.Comment: 5 pages, 2 figure

In situ characterization of qubit control lines: a qubit as a vector network analyzer

We present a technique to measure the transfer function of a control line using a qubit as a vector network analyzer. Our method requires coupling the line under test to the the longitudinal component of the Hamiltonian of the qubit and the ability to induce Rabi oscillations through simultaneous driving of the transversal component. We used this technique to characterize the 'flux' control of a superconducting Transmon qubit in the range of 8 to 400\,MHz. Our method can be used for the qubit 'flux' line calibration to increase the fidelity of entangling gates for the quantum processor. The qubit can be also used as a microscopic probe of the electro-magnetic fields on a chip.Comment: 5 pages, 4 figure

Resonant all-electric spin pumping with spin-orbit coupling

All-electric devices for the generation and filtering of spin currents are of crucial importance for spintronics experiments and applications. Here we consider a quantum dot between two metallic leads in the presence of spin-orbit coupling, and we analyze in the frame of a scattering matrix approach the conditions for generating spin currents in an adiabatically driven two-terminal device. We then focus on a dot with two resonant orbitals and show by specific examples that both spin filtering and pure spin current generation can be achieved. Finally, we discuss the effect of the Coulomb interaction.Comment: 4 pages, corrected typo in list of author

Visual speech alters the discrimination and identification of non-intact auditory speech in children with hearing loss

OBJECTIVES: Understanding spoken language is an audiovisual event that depends critically on the ability to discriminate and identify phonemes yet we have little evidence about the role of early auditory experience and visual speech on the development of these fundamental perceptual skills. Objectives of this research were to determine 1) how visual speech influences phoneme discrimination and identification; 2) whether visual speech influences these two processes in a like manner, such that discrimination predicts identification; and 3) how the degree of hearing loss affects this relationship. Such evidence is crucial for developing effective intervention strategies to mitigate the effects of hearing loss on language development. METHODS: Participants were 58 children with early-onset sensorineural hearing loss (CHL, 53% girls, M = 9;4 yrs) and 58 children with normal hearing (CNH, 53% girls, M = 9;4 yrs). Test items were consonant-vowel (CV) syllables and nonwords with intact visual speech coupled to non-intact auditory speech (excised onsets) as, for example, an intact consonant/rhyme in the visual track (Baa or Baz) coupled to non-intact onset/rhyme in the auditory track (/–B/aa or /–B/az). The items started with an easy-to-speechread /B/ or difficult-to-speechread /G/ onset and were presented in the auditory (static face) vs. audiovisual (dynamic face) modes. We assessed discrimination for intact vs. non-intact different pairs (e.g., Baa:/–B/aa). We predicted that visual speech would cause the non-intact onset to be perceived as intact and would therefore generate more same—as opposed to different—responses in the audiovisual than auditory mode. We assessed identification by repetition of nonwords with non-intact onsets (e.g., /–B/az). We predicted that visual speech would cause the non-intact onset to be perceived as intact and would therefore generate more Baz—as opposed to az— responses in the audiovisual than auditory mode. RESULTS: Performance in the audiovisual mode showed more same responses for the intact vs. non-intact different pairs (e.g., Baa:/–B/aa) and more intact onset responses for nonword repetition (Baz for/–B/az). Thus visual speech altered both discrimination and identification in the CHL—to a large extent for the /B/ onsets but only minimally for the /G/ onsets. The CHL identified the stimuli similarly to the CNH but did not discriminate the stimuli similarly. A bias-free measure of the children’s discrimination skills (i.e., d’ analysis) revealed that the CHL had greater difficulty discriminating intact from non-intact speech in both modes. As the degree of HL worsened, the ability to discriminate the intact vs. non-intact onsets in the auditory mode worsened. Discrimination ability in CHL significantly predicted their identification of the onsets—even after variation due to the other variables was controlled. CONCLUSIONS: These results clearly established that visual speech can fill in non-intact auditory speech, and this effect, in turn, made the non-intact onsets more difficult to discriminate from intact speech and more likely to be perceived as intact. Such results 1) demonstrate the value of visual speech at multiple levels of linguistic processing and 2) support intervention programs that view visual speech as a powerful asset for developing spoken language in CHL

Children perceive speech onsets by ear and eye*

Adults use vision to perceive low-fidelity speech; yet how children acquire this ability is not well understood. The literature indicates that children show reduced sensitivity to visual speech from kindergarten to adolescence. We hypothesized that this pattern reflects the effects of complex tasks and a growth period with harder-to-utilize cognitive resources, not lack of sensitivity. We investigated sensitivity to visual speech in children via the phonological priming produced by low-fidelity (non-intact onset) auditory speech presented audiovisually (see dynamic face articulate consonant/rhyme b/ag; hear non-intact onset/rhyme: −b/ag) vs. auditorily (see still face; hear exactly same auditory input). Audiovisual speech produced greater priming from four to fourteen years, indicating that visual speech filled in the non-intact auditory onsets. The influence of visual speech depended uniquely on phonology and speechreading. Children – like adults – perceive speech onsets multimodally. Findings are critical for incorporating visual speech into developmental theories of speech perception

Realization of a quantum random generator certified with the Kochen-Specker theorem

Random numbers are required for a variety of applications from secure communications to Monte\ua0Carlo simulation. Yet randomness is an asymptotic property, and no output string generated by a physical device can be strictly proven to be random. We report an experimental realization of a quantum random number generator (QRNG) with randomness certified by quantum contextuality and the Kochen-Specker theorem. The certification is not performed in a device-independent way but through a rigorous theoretical proof of each outcome being value indefinite even in the presence of experimental imperfections. The analysis of the generated data confirms the incomputable nature of our QRNG

Phonological Priming in Children with Hearing Loss:Effect of Speech Mode, Fidelity, and Lexical Status

OBJECTIVES: Our research determined 1) how phonological priming of picture naming was affected by the mode (auditory-visual [AV] vs auditory), fidelity (intact vs non-intact auditory onsets), and lexical status (words vs nonwords) of speech stimuli in children with prelingual sensorineural hearing impairment (CHI) vs. children with normal hearing (CNH); and 2) how the degree of hearing impairment (HI), auditory word recognition, and age influenced results in CHI. Note that some of our AV stimuli were not the traditional bimodal input but instead they consisted of an intact consonant/rhyme in the visual track coupled to a non-intact onset/rhyme in the auditory track. Example stimuli for the word bag are: 1) AV: intact visual (b/ag) coupled to non-intact auditory (−b/ag) and 2) Auditory: static face coupled to the same non-intact auditory (−b/ag). Our question was whether the intact visual speech would “restore or fill-in” the non-intact auditory speech in which case performance for the same auditory stimulus would differ depending upon the presence/absence of visual speech. DESIGN: Participants were 62 CHI and 62 CNH whose ages had a group-mean and -distribution akin to that in the CHI group. Ages ranged from 4 to 14 years. All participants met the following criteria: 1) spoke English as a native language, 2) communicated successfully aurally/orally, and 3) had no diagnosed or suspected disabilities other than HI and its accompanying verbal problems. The phonological priming of picture naming was assessed with the multi-modal picture word task. RESULTS: Both CHI and CNH showed greater phonological priming from high than low fidelity stimuli and from AV than auditory speech. These overall fidelity and mode effects did not differ in the CHI vs. CNH—thus these CHI appeared to have sufficiently well specified phonological onset representations to support priming and visual speech did not appear to be a disproportionately important source of the CHI’s phonological knowledge. Two exceptions occurred, however. First—with regard to lexical status—both the CHI and CNH showed significantly greater phonological priming from the nonwords than words, a pattern consistent with the prediction that children are more aware of phonetics-phonology content for nonwords. This overall pattern of similarity between the groups was qualified by the finding that CHI showed more nearly equal priming by the high vs. low fidelity nonwords than the CNH; in other words, the CHI were less affected by the fidelity of the auditory input for nonwords. Second, auditory word recognition—but not degree of HI or age—uniquely influenced phonological priming by the nonwords presented AV. CONCLUSIONS: With minor exceptions, phonological priming in CHI and CNH showed more similarities than differences. Importantly, we documented that the addition of visual speech significantly increased phonological priming in both groups. Clinically these data support intervention programs that view visual speech as a powerful asset for developing spoken language in CHI

Nonreciprocity realized with quantum nonlinearity

Nonreciprocal devices are a key element for signal routing and noise isolation. Rapid development of quantum technologies has boosted the demand for a new generation of miniaturized and low-loss nonreciprocal components. Here we use a pair of tunable superconducting artificial atoms in a 1D waveguide to experimentally realize a minimal passive nonreciprocal device. Taking advantage of the quantum nonlinear behavior of artificial atoms, we achieve nonreciprocal transmission through the waveguide in a wide range of powers. Our results are consistent with theoretical modeling showing that nonreciprocity is associated with the population of the two-qubit nonlocal entangled quasi-dark state, which responds asymmetrically to incident fields from opposing directions. Our experiment highlights the role of quantum correlations in enabling nonreciprocal behavior and opens a path to building passive quantum nonreciprocal devices without magnetic fields