26 results for qubit oscillator frequency
Contributors: Sigillito, Anthony James, Lyon, Stephen A, Electrical Engineering Department
frequency and double quantum transitions (magnetic-dipole forbidden...qubit onto and off of resonance with a magnetic driving field. In this...Qubits...qubits....qubit coherence times should substantially increase. Finally,...qubits. Here, single qubit addressability becomes an issue. Ideally...qubits is the electron spin bound to phosphorus donors in silicon...frequencies or lower temperatures the qubit coherence times should...qubit addressability. First, we demonstrate that nuclear spin...Qubits in Silicon and Germanium ... Many proposals for quantum information devices rely on electronic or nuclear spins in semiconductors because of their long coherence times and compatibility with industrial fabrication processes. One of the most notable qubits is the electron spin bound to phosphorus donors in silicon, which offers coherence times exceeding seconds at low temperatures. These donors are naturally isolated from their environments to the extent that silicon has been coined a "semiconductor vacuum". While this makes for ultra-coherent qubits, it is difficult to couple two remote donors so quantum information proposals rely on high density arrays of qubits. Here, single qubit addressability becomes an issue. Ideally one would address individual qubits using electric fields which can be easily confined. Typically these schemes rely on tuning a donor spin qubit onto and off of resonance with a magnetic driving field. In this thesis, we measure the electrical tunability of phosphorus donors in silicon and use the extracted parameters to estimate the effects of electric-field noise on qubit coherence times. Our measurements show that donor ionization may set in before electron spins can be sufficiently tuned. We therefore explore two alternative options for qubit addressability. First, we demonstrate that nuclear spin qubits can be directly driven using electric fields instead of magnetic fields and show that this approach offers several advantages over magnetically driven spin resonance. In particular, spin transitions can occur at half the spin resonance frequency and double quantum transitions (magnetic-dipole forbidden) can occur. In a second approach to realizing tunable qubits in semiconductors, we explore the option of replacing silicon with germanium. We first measure the coherence and relaxation times for shallow donor spin qubits in natural and isotopically enriched germanium. We find that in isotopically enriched material, coherence times can exceed 1 ms and are limited by a single-phonon T1 process. At lower frequencies or lower temperatures the qubit coherence times should substantially increase. Finally, we measure the electric field tunability of donors in germanium and find a four order-of-magnitude enhancement in the spin-orbit Stark shift and confirm that the donors should be tunable by at least 4 times the electron spin ensemble linewidth (in isotopically enriched material). Germanium should therefore also be more sensitive to electrically driven nuclear magnetic resonance. Based on these results germanium is a promising alternative to silicon for spin qubits.
Contributors: Srinivasan, Srikanth, Houck, Andrew, Electrical Engineering Department
Qubits...qubit (TCQ), to the toolbox available for exploring such physics. The ...qubit energy and dipole coupling strength. High frequency flux control...qubit energy and dipole coupling strength. High frequency flux control...qubit coherence measurements and the calculation of a lower bound on the ... Superconducting circuits have shown promise for exploring quantum optics and computing. This thesis presents an additional element, the tunable coupling qubit (TCQ), to the toolbox available for exploring such physics. The TCQ is shown to have independently tunable qubit energy and dipole coupling strength. High frequency flux control lines allow the varying of the TCQ's properties on very fast time scales. This enables qubit coherence measurements and the calculation of a lower bound on the maximum range of coupling strength tunability. Finally, an experiment demonstrating the TCQ's applicability in quantum state transfer is discussed.
Probing the relationship between high frequency oscillations and epileptic brain activity through the lens of feedforward inhibition
Contributors: Fan, Jaimie, Buschman, Timothy J.
frequency oscillations occur in the brains of those with epilepsy does...frequency oscillation remains an open question. However, in the process...frequency oscillation between epileptic and non-epileptic brains can be...frequency oscillations occur in both the brains of those with epilepsy...frequency oscillation on various weight combinations within the phase ... The current variety of treatment options for epilepsy leaves 30% of those who suffer from this chronic neurological disease without a cure. Therefore, this senior thesis project aims to uncover new insights about the brain structure that underlies susceptibility to epilepsy in hopes that a greater understanding of this underlying structure will catalyze the discovery of novel therapeutic methods which target these underlying differences in brain structure. To drive the discovery of new insights about underlying structure, this project addresses the following tension found in the literature: high frequency oscillations occur in both the brains of those with epilepsy and in the brains of those without epilepsy. Only when high frequency oscillations occur in the brains of those with epilepsy does the brain enter a state of unstable dynamics and seizure activity. This suggests that there is a difference in underlying structure between epileptic and non-epileptic brains, and this study uses computational modeling of neuronal firing to characterize these differences. First, based on a firing rate model, we find that within the phase space of the weight values, there is a band of stability from which one might predict the stability of a set of weights. Then, in the next two versions of the model, we add Hebbian plasticity and homeostatic plasticity. Only through the addition of Hebbian plasticity and homeostatic plasticity does high frequency oscillation, the manipulation described in our driving question, have a lasting effect on the weights. With the addition of a rate based Hebbian plasticity model to the base firing rate model, we find that weights can be perturbed from this band of stability through Hebbian plasticity. Adding a weight based homeostatic plasticity model to the base firing rate and Hebbian plasticity model then gives insight into the fact that having a target weight within a certain location with respect to the band of stability can rescue stability of a set of original weights from the destabilizing effects of Hebbian plasticity. Finally, we explore the effect of high frequency oscillation on various weight combinations within the phase space, and we find that certain weight combinations are projected to an unstable state through high frequency oscillation while other weight combinations remain at a stable state even in the face of high frequency oscillation. The unifying characteristic of those weights which remain stable in the face of high frequency oscillation remains an open question. However, in the process of investigating high frequency oscillations, it was found that weights on the edge of the band of stability are more robust to instability through Hebbian plasticity than weights on the band of stability that are further from the edge. These results suggest that the differential response to high frequency oscillation between epileptic and non-epileptic brains can be attributed at least in part to the location of weights with respect to the band of stability.
Contributors: Szócs, László J., Houck, Andrew
Photon-Qubit Coupling...qubits. Both qubit devices failed to exhibit signs of light-matter coupling...cavity-qubit dynamics in the multimodal regime for various light-matter...frequency ¿0/(2¿) = 92 MHz, two of which contained superconducting transmon ... This thesis presents the results of experimental work aimed at realizing the multimodal Rabi Hamiltonian of quantum optics in a circuit QED device. We have fabricated and tested three coplanar waveguide resonators of fundamental frequency ¿0/(2¿) = 92 MHz, two of which contained superconducting transmon qubits. Both qubit devices failed to exhibit signs of light-matter coupling, as deduced through two different measurement techniques. The experimental progress was supplemented with numerical simulations of the multimodal Jaynes-Cummings and Rabi Hamiltonians, which attempted to study cavity-qubit dynamics in the multimodal regime for various light-matter coupling strengths. For a 2-mode Rabi model, we report the observation of a novel localization-delocalization transition in photon occupation between the two modes, which displays signatures that should be readily measured in experiment. Future work should continue attempts to realize strong, multimodal light-matter coupling in circuit QED so as to verify the existence of this transition.
Skirting the Limits of Speech Intelligibility The Role of Theta-Oscillations in Decoding Degraded Speech: A Behavioral and Electrocorticographical Study of the Auditory Pop-Out Effect
Contributors: Martin, Christan David, Hasson, Uri, Ghazanfar, Asif
Oscillations are present both in natural speech and in the brain. This...theta-frequency band oscillations for speech comprehension as well as ...theta-frequency band has been shown to remarkably improve intelligibility...theta-frequency range can restore intelligibility to a degraded, previously...theta-frequency oscillations in auditory regions, specifically the superior ... Oscillations are present both in natural speech and in the brain. This may be more than a mere coincidence. Re-instating information in the theta-frequency band has been shown to remarkably improve intelligibility. Moreover, a recent theory has proposed the existence of an internal tracking mechanism that parses and decodes incoming speech at a theta rhythm. This study sought to clarify the importance of theta-frequency band oscillations for speech comprehension as well as to establish their significance as a speech processing mechanism in the human auditory cortex. Here, it is shown that exposure to information in the theta-frequency range can restore intelligibility to a degraded, previously unintelligible stimulus, producing an auditory pop-out effect. This effect was observed regardless of whether participants were exposed to the intact sentence in the auditory or the visual domain. Compressing or extending the presentation speed of the intact sentence reduced the size of the effect, except for an extension rate of 1.5 times the original speed. At a neural level, it was previously unknown whether theta oscillations in auditory regions are internally generated or merely reflect stimulus driven evoked responses. Electrocorticographical recordings from one clinical patient provide evidence for the existence of theta-frequency oscillations in auditory regions, specifically the superior temporal gyrus, which are internally generated and effectively track incoming speech.
Contributors: Siow, Matthew, Couzin, Iain
oscillation frequency compared to the other two zones of the same junction...oscillations that allow it to gain maximum stability. In this paper, we...oscillations at trail junctions to determine how army ants optimize their...oscillation frequencies and periods of army ant traffic are uniform and...oscillation frequency increases as traffic becomes more unidirectional ... Army ants (Eciton burchellii) have been studied for nearly a century, but observable patterns in their traffic organization have not yet been explored, despite the fact that this organization contributes greatly to their optimal foraging. Using pheromones and tactile cues to transmit information from ant to ant, they coordinate their movements in order to optimize traffic and create a collective behavior that increases the overall efficiency of the colony. Garnier et al. (2013) discovered that E. burchellii traffic possesses regular, periodic oscillations that allow it to gain maximum stability. In this paper, we explored these traffic oscillations at trail junctions to determine how army ants optimize their network of foraging trails. After conducting research at La Selva Biological Station in Costa Rica, we found that the mean oscillation frequencies and periods of army ant traffic are uniform and unrelated to traffic direction. Despite this overarching uniformity, each zone of a trail junction possesses a different oscillation frequency compared to the other two zones of the same junction. Lastly, oscillation frequency increases as traffic becomes more unidirectional. By displaying differential oscillatory behavior at trail junctions, army ants spontaneously adapt to their constantly changing environment in order to optimize traffic dynamics. Finally, we propose ideas for future research that have the potential to delve deeper into the study of trail junctions.
Contributors: Zhang, Gengyan, Houck, Andrew A, Electrical Engineering Department
multi-qubit system where crosstalk between qubits causes error in quantum...two-qubit device and suppress crosstalk by tuning the ZZ coupling rate...qubits against noise. We implement a qubit whose frequency and dispersive...qubits. The tunable dispersive coupling can also be parametrically modulated...qubits causes error in quantum gates. We develop a two-qubit device and...qubits against noise. We implement a qubit whose frequency and dispersive...qubit becomes immune to photon number fluctuations in the resonator and...two-qubit entangling gate in the low crosstalk regime. Those devices provide ... Circuit quantum electrodynamics (cQED) uses superconducting circuit elements as its building blocks for controllable quantum systems and has become a promising experimental platform for quantum computation and quantum simulation. The ability to tune the coupling rate between circuit elements extends the controllability and flexibility of cQED devices and can be utilized to improve device performance. This thesis presents the study, implementation and application of tunable coupling devices in cQED. The tunability originates from the basic principles of quantum superposition and interference, and unwanted interactions can be suppressed by destructive interference. Following this principle, we design and conduct two experiments that demonstrate the utility of tunable coupling for better device performances in quantum information processing. The first experiment aims to improve the coherence of qubits against noise. We implement a qubit whose frequency and dispersive coupling to a readout resonator can be tuned independently. When the coupling rate is tuned to near zero, the qubit becomes immune to photon number fluctuations in the resonator and exhibits robust coherence time in the presence of noise. The second experiment extends to a multi-qubit system where crosstalk between qubits causes error in quantum gates. We develop a two-qubit device and suppress crosstalk by tuning the ZZ coupling rate between the qubits. The tunable dispersive coupling can also be parametrically modulated to implement a two-qubit entangling gate in the low crosstalk regime. Those devices provide flexible and promising building blocks for cQED systems.
Contributors: Sundaresan, Neereja Mythili, Houck, Andrew A, Electrical Engineering Department
qubit detuning from the band-edge, offering an avenue of in situ control...qubit is simultaneously strongly coupled to a large, but discrete number...qubit to a low fundamental frequency coplanar waveguide cavity. In this...qubits strongly coupled to photonic crystals, which give rise to exotic...qubits to spectrally structured media using superconducting circuits...qubits, and the qubits themselves. The localization of these states changes...qubit mediated mode-mode interactions. In the second...qubit-photon dressed bound states comprising induced, spatially localized...qubit to a low fundamental frequency coplanar waveguide cavity. In this ... The advent of superconducting quantum circuits as a robust scientific platform and contender for quantum computing applications is the result of decades of research in light-matter interaction, low-temperature physics, and microwave engineering. There is growing interest to use this advancing technology to study domains of light-matter interaction that were previously thought to be beyond experimental reach. Our work is part of an initiative to explore non-equilibrium condensed matter physics using photons instead of atoms. Open questions in this area currently pose significant challenges theoretically due to analytical complexity and system sizes which prohibit complete numerical simulations, thus experiment-based research has the potential to lead to significant advancements in this field. Here we examine phenomena that arise when moving beyond standard single-mode strong coupling towards the realm of many-body physics with light in two distinct directions. First we study multimode strong coupling, where a single artificial atom or qubit is simultaneously strongly coupled to a large, but discrete number of non-degenerate photonic modes of a cavity with coupling strengths comparable to the free spectral range. This domain, which falls in between small, discrete and continuum Hilbert spaces, is experimentally realized by coupling a qubit to a low fundamental frequency coplanar waveguide cavity. In this system we report on resonance fluorescence and narrow linewidth emission directly resulting from complex qubit mediated mode-mode interactions. In the second part we explore qubits strongly coupled to photonic crystals, which give rise to exotic physical scenarios, beginning with single and multi-excitation qubit-photon dressed bound states comprising induced, spatially localized photonic modes, centered around the qubits, and the qubits themselves. The localization of these states changes with qubit detuning from the band-edge, offering an avenue of in situ control of bound state interaction. Due to their localization-dependent interaction, these states offer the ability to create one-dimensional chains of bound states with tunable interactions that preserve the qubits' spatial organization, a key criterion for realization of certain quantum many-body models. The unique domains of light-matter interaction discussed here are a subset of exciting research initiatives growing our general understanding of complex, strongly coupled quantum systems.
Contributors: Johnsen, Peter, Houck, Andrew A., Bernevig, Bogdan A.
qubit energy, demonstrating that we are in the strong coupling qubit-field...qubit based on the Josephson junction. We observe photon number splitting...qubit, we will be able to realize strong photon-photon interactions for...qubit excitation. This system can exhibit behavior known as photon blockade...frequency shift ¿, we are unable to observe photon blockade or measure...qubit to a region of the transmission line with a higher electric field ... Superconducting circuits are an ideal platform for simulating many body physics with photons. Such simulations are greatly enhanced by the ability to engineer photon-photon interactions. Single photon-photon interactions are difficult to design because of the massive nonlinearities required to achieve a strong interaction between individual photons. Nonlinearities arising from single photons are present in the dispersive limit of Jaynes-Cummings Hamiltonian. In this limit, the interaction of two photons is mediated by a virtual qubit excitation. This system can exhibit behavior known as photon blockade, where the presence of a single photon in an optical cavity prevents other photons from entering the cavity. The light exiting the cavity is then antibunched, which serves both as evidence of the quantization of the electromagnetic field and as a signature of photon blockade. Experimentally, we explore the strong qubit-field coupling regime of the Jaynes-Cummings Hamiltonian with circuit quantum electrodynamics. Using conventional microfabrication techniques, we build a superconducting microwave resonator coupled to a transmon qubit based on the Josephson junction. We observe photon number splitting of the qubit energy, demonstrating that we are in the strong coupling qubit-field coupling regime, allowing us to perform quantum non-demolition measurements of the cavity photon number, and providing conclusive evidence of the quantization of the electromagnetic field into photons. Further, we observe nonlinear effects arising from a small photon number consistent with the nonlinear Kerr Hamiltonian approximation of the Jaynes-Cummings Hamiltonian. Because the cavity dissipation ¿ is larger than the single photon cavity frequency shift ¿, we are unable to observe photon blockade or measure photon antibunching. By moving the qubit to a region of the transmission line with a higher electric field and using a tunable SQUID (superconducting quantum interference device) as a qubit, we will be able to realize strong photon-photon interactions for use in quantum simulators.
Contributors: Dewey, Peter, Smits, Alexander J, Mechanical and Aerospace Engineering Department
frequency and wake resonant frequencies are finite, this also suggests...frequencies. It is found that when the driving oscillation frequency ...frequency of the flexible structure is coincident with the wake resonant...frequency there is a local peak in propulsive efficiency. The global ...oscillation frequency and chordwise traveling wave wavelength that develops ... Experiments are conducted to better understand the effects of flexibility in generating unsteady bio-inspired propulsion. It is found that by exploiting the effects of flexibility, the thrust production and propulsive efficiency can be up to twice that of a rigid propulsor. The wakes are highly dependent on the input parameters to the system such as the oscillation frequency and chordwise traveling wave wavelength that develops along a flexible surface. In general, the wakes of flexible propulsors tend to concentrate their momentum in the direction of motion whereas the wakes of rigid propulsors have relatively larger momentum in the transverse direction leading to a decrease in propulsive efficiency. A linear stability analysis is conducted on the wakes to determine the wake resonant frequencies. It is found that when the driving oscillation frequency of the apparatus matches the wake resonant frequency there is a local peak in propulsive efficiency. The global peak in efficiency occurs only when the structural resonant frequency of the flexible structure is coincident with the wake resonant frequency, which only occurs under very specific conditions. This implies that there is an optimum flexibility to maximize propulsive efficiency; being either too stiff or too flexible is detrimental to propulsive performance. Since both the structural resonant frequency and wake resonant frequencies are finite, this also suggests that animals must utilize flexible propulsive surfaces if they are to optimize their efficiencies. Finally, a non-dimensional scaling argument is made that is shown to collapse the thrust production, power input to the fluid, and propulsive efficiency for a range of propulsors with various flexibilities and aspect ratio.