Download or read book Development of a Silicon Semiconductor Quantum Dot Qubit with Dispersive Microwave Readout written by Edward Trowbridge Henry and published by . This book was released on 2013 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductor quantum dots in silicon demonstrate exceptionally long spin lifetimes as qubits and are therefore promising candidates for quantum information processing. However, control and readout techniques for these devices have thus far employed low frequency electrons, in contrast to high speed temperature readout techniques used in other qubit architectures, and coupling between multiple quantum dot qubits has not been satisfactorily addressed. This dissertation presents the design and characterization of a semiconductor charge qubit based on double quantum dot in silicon with an integrated microwave resonator for control and readout. The 6 GHz resonator is designed to achieve strong coupling with the quantum dot qubit, allowing the use of circuit QED control and readout techniques which have not previously been applicable to semiconductor qubits. To achieve this coupling, this document demonstrates successful operation of a novel silicon double quantum dot design with a single active metallic layer and a coplanar stripline resonator with a bias tee for dc excitation. Experiments presented here demonstrate quantum localization and measurement of both electrons on the quantum dot and photons in the resonator. Further, it is shown that the resonator-qubit coupling in these devices is sufficient to reach the strong coupling regime of circuit QED. The details of a measurement setup capable of performing simultaneous low noise measurements of the resonator and quantum dot structure are also presented here. The ultimate aim of this research is to integrate the long coherence times observed in electron spins in silicon with the sophisticated readout architectures available in circuit QED based quantum information systems. This would allow superconducting qubits to be coupled directly to semiconductor qubits to create hybrid quantum systems with separate quantum memory and processing components.

Download or read book Dispersive Readout of Industrially fabricated Silicon Quantum Dots written by David J. Ibberson and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Understanding and Suppressing Dephasing Noise in Semiconductor Qubits written by Félix Beaudoin and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Magnetic-field gradients and microwave resonators are promising tools to realize a scalable quantum-computing architecture with spin qubits. Indeed, magnetic-field gradients allow fast selective manipulation of distinct qubits through electric-dipole spin resonance and coherent coupling of spin qubits to a microwave resonator. On the other hand, microwave resonators are useful for quantum state transfer and two-qubit gates between distant qubits, and qubit readout. In this thesis, we take a theoretical approach to understand and suppress pure-dephasing mechanisms relevant to spin qubits in the presence of the above-mentioned devices, recently introduced to improve scalability. We first focus on dephasing of a spin qubit in the presence of a magnetic-field gradient. We predict that hyperfine coupling of the qubit to an environment of nuclear spins precessing under the influence of a magnetic-field gradient leads to a new qubit dephasing mechanism. We show that in realistic conditions, this new mechanism can dominate over the usual dephasing processes occurring in the absence of a gradient. This result is relevant to spin qubits in GaAs or silicon quantum dots, or at single phosphorus donors in silicon. A magnetic-field gradient may also expose spin qubits to charge noise. We thus also study microscopic charge dephasing mechanisms coming from two-level fluctuators. These mechanisms typically lead to qubit coherence decay of the form exp[-(t/T2)^alpha]. Focusing on processes coupling charge fluctuators to electron or phonon baths, we find distinct dependencies of T2 and alpha on temperature depending on the nature of the fluctuator-bath interaction. These predictions may be useful for experimental identification of physical processes leading to charge dephasing of semiconductor qubits, and offer a new perspective to better understand the results of a recent experiment [Dial et al. Phys. Rev. Lett. 110:146804 (2013)]. Finally, we develop and assess a new protocol for quantum state transfer between a qubit and a resonator that has a high fidelity even in the presence of strong dephasing from low-frequency noise caused, e.g., by nuclear-spin or charge noise. In addition, upon a small modification of our state-transfer protocol, we obtain a method for fast quantum nondemolition readout of a qubit through the resonator output field. This new approach leads to a high-fidelity readout even when resonator damping is stronger than the qubit-resonator coupling. These two improved quantum operations (state transfer and readout) are particularly relevant for spin qubits coupled to microwave resonators, since spin-resonator coupling is typically weaker than qubit dephasing and resonator damping." --

Download or read book Advancement of Silicon based Spin Qubits written by Elliot Connors and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Electron spins in gate-defined quantum dots have emerged as a leading candidate for quantum-information-processing applications, including quantum computation. Long coherence times and compatibility with conventional semiconductor-manufacturing techniques contribute to the appeal of implementing these devices as quantum bits, or qubits. Recent research efforts have demonstrated many of the fundamental requirements for their utilization in a future quantum processor. Despite this, further development in the performance of these devices is necessary if the goal is truly to realize a universal quantum computer. Improvements will likely come in the form of both device-engineering advancements as well as novel qubit-operation and qubit-measurement schemes. This thesis describes a number of experiments carried out in gate-defined quantum dots in Si/SiGe, including demonstrations of high-fidelity spin-measurement, multiple studies of environmental noise, and coherent control of electron-spin qubits. This work represents the first realization of such devices in the Nichol Group at the University of Rochester. Together, the results represent the advancement of our understanding of silicon-based quantum dots and spin qubits"--Page xii.

Download or read book Dispersive Readout and Spin state Spectroscopy of Industrially fabricated Silicon Quantum Dots written by Theodor William Lundberg and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Investigation of Silicon Metal oxide semiconductor Based Triple Quantum Dot written by Hong Pan and published by . This book was released on 2013 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the rapid progress in nanofabrication, scientists and researchers are now able to make lateral quantum dots in semiconductor materials. The few electrons confined in these quantum dots provide the possibility of realizing a qubit, the building block of a quantum computer. Tremendous effort has been put in the solid state quantum information field in the last ten years of making single electron spin qubit or singlet triplet qubit based on two electron spin. However, the operation of these types of qubit requires additional engineering by either integrating a microwave loop or an external magnet to creat field difference. This thesis project was inspired by DiVincenzo's proposal of developing qubit based on three electrons controlled by Heisenberg exchange interactions only, which is called "exchange-only" qubit. All the qubit operation can be done in principle via electrical pulses only. We proposed to make the triple quantum device in silicon system. This type of device will have small qubit decoherence, easy integration to industry infrustructure and great chance of scaling up to a real quantum computer. We developed and fabricated the electrostatically defined triple quantum dot (TQD) device in a silicon metal-oxide-oxide structure. We characterized its electrostatic properties using a quantum point contact charge sensing channel nearby. We are be able to obtain the charge stability diagram in the last few elelctron regime that provides the experimental basis of forming a exchange only qubit. We demonstrated the tunability of the TQD by acheiving the quadruple points where all three dots are on resonance. This is the first experimental demonstration of well controlled triple quantum dot device in silicon system. The constant interaction model and the hubbard model for triple quantum dot system are developed to help understand the electrostatic dynamics. Tunnel couplings between quantum dots, which determines the exchange interactions, are extracted using various fitting methods. We implemented the qubit manipulation with three quantum dots in both a linearly and a triangularly arranged geometry. For the first time, we observed coherent oscillation in the Si MOS based triple quantum dot device with oscillation frequency of 2MHz and 7MHz. We suspect the these oscillations are related with spin dynamics in our system. These experimental investigations demonstrate that we have the ability to develop triple quantum dot device for exchange ony qubit and the potential to perform qubit operation in the future.

Download or read book Microwave driven Coherent Operation of a Semiconductor Quantum Dot Charge Qubit written by and published by . This book was released on 2015 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: An intuitive realization of a qubit is an electron charge at two well-defined positions of a double quantum dot. The qubit is simple and has the potential for high-speed operation because of its strong coupling to electric fields. But, charge noise also couples strongly to this qubit, resulting in rapid dephasing at all but one special operating point called the 'sweet spot'. In previous studies d.c. voltage pulses have been used to manipulate semiconductor charge qubits but did not achieve high-fidelity control, because d.c. gating requires excursions away from the sweet spot. Here, by using resonant a.c. microwave driving we achieve fast (greater than gigahertz) and universal single qubit rotations of a semiconductor charge qubit. The Z-axis rotations of the qubit are well protected at the sweet spot, and we demonstrate the same protection for rotations about arbitrary axes in the X-Y plane of the qubit Bloch sphere. We characterize the qubit operation using two tomographic approaches: standard process tomography and gate set tomography. Moreover, both methods consistently yield process fidelities greater than 86% with respect to a universal set of unitary single-qubit operations.

Download or read book Analysis of Readout Measurements for Silicon based Quantum dot Spin Qubits written by 林嗣智 and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dispersive Readout of a Superconducting Qubit Using a Slug Amplifier written by and published by . This book was released on 2013 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing a fast, high-fidelity readout of superconducting quantum bits (qubits) makes significant demands of the cryogenic amplification chain, where the first stage ampli- fier must have sufficient sensitivity to resolve the state of the qubit and enough gain to overcome the noise of subsequent stages of amplification. Additionally, the architecture of a scalable quantum computer requires an amplifier with a large enough bandwidth and dynamic range to simultaneously measure multiple qubits without sacrificing perfor- mance. In this thesis, we describe a novel low-noise phase-insensitive linear amplifier at microwave frequencies based on the Superconducting Low-Inductance Undulatory Gal- vanometer (SLUG), an amplifier capable of meeting the demands of the superconducting qubit community. We discuss the numerical optimization of the SLUG amplifier and cal- culate the expected amplifier gain and noise temperature. We walk through the amplifier design and fabrication process before discussing how to fully characterize the fabricated device. We report on amplifiers with measured gain of 10 to 15 dB, bandwidths from 50 to 100 MHz, and added system noise below 2 quanta. Next, we describe the qubit- cavity system and the limits of a dispersive quantum measurement using circuit quantum electrodynamics. Finally, we report on experiments where a SLUG amplifier is used to measure the state of a superconducting qubit, demonstrating improved measurement signal-to-noise ratios of 10 dB and a dynamic range that is an order of magnitude better than any available amplifier currently being developed.

Download or read book Solid State Quantum Computing Using Spin Qubits in Silicon Quantum Dots QCCM written by and published by . This book was released on 2009 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: The project goals are to fabricate qubits in quantum dots in Si/SiGe modulation-doped heterostructures, to characterize and understand those structures, and to develop the technology necessary for a Si/SiGe quantum dot quantum computer. The physical qubit in our approach is the spin of an electron confined in a top-gated silicon quantum dot in a Si/SiGe modulation-doped heterostructure. Operations on such a qubit may be performed by controlling the voltages on gates in-between neighboring quantum dots. A quantum computer and qubits in silicon offer potential advantages, both fundamental and practical. Electron spins in silicon quantum dots are expected to have long coherence times. Silicon has an isotope, Si, which has zero nuclear spin and thus no nuclear magnetic moment. As a result, electron spins in silicon have longer coherence times than they would in the presence of a fluctuating nuclear spin background. From a practical perspective, modern classical computers are made in silicon, and one hopes that this will lead to synergy in the future with a silicon quantum computer. This QCCM includes both theory and experiment focusing on (i) the development of qubits in the form of electron spins in silicon quantum dots, (ii) the measurement and manipulation of those qubits, and (iii) the science essential for understanding the properties of such qubits.

Download or read book Theoretical Issues in Silicon Quantum Dot Qubits written by and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrically-gated quantum dots in semiconductors is an excellent architecture on which to make qubits for quantum information processing. Silicon is attractive because of the potential for excellent manipulability, scalability, and for integration with classical electronics. This thesis describes several aspects of the theoretical issues related to quantum dot qubits in silicon. It may be broadly divided into three parts -- (1) the hybrid qubit and quantum gates, (2) decoherence and (3) charge transport. In the first part, we present a novel architecture for a double quantum dot spin qubit, which we term the hybrid qubit, and demonstrate that implementing this qubit in silicon is feasible. Next, we consider both AC and DC quantum gating protocols and compare the optimal fidelities for these protocols that can be achieved for both the hybrid qubit and the more traditional singlet-triplet qubit. In the second part, we present evidence that silicon offers superior coherence properties by analyzing experimental data from which charge dephasing and spin relaxation times are extracted. We show that the internal degrees of freedom of the hybrid qubit enhance charge coherence, and demonstrate tunable spin loading of a quantum dot. In the last part, we explain three key features of spin-dependent transport -- spin blockade, lifetime-enhanced transport and spin-flip cotunneling. We explain how these features arise in the conventional two-electron as well as the unconventional three-electron regimes, using a theoretical model that captures the key characteristics observed in the data.

Download or read book Coherent Manipulation of Semiconductor Quantum Dot Qubits written by John Rooney and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum computing has received growing interest not only from the research community, but also in the general public. One reason for this focus is due to the ability of a quantum computer to solve problems that cannot be computed classically, creating a pathway for solutions to complex problems that would benefit numerous aspects of society. One of the popular proposals for a quantum computer harnesses semiconductor quantum dots to define qubits within electron or hole states. Due to the compatibility of this technology with existing nanoscale industrial fabrication facilities, it has a unique advantage of being able to scale to the millions of qubits required for a commercially practical quantum computer. Within this work, I will describe two approaches to building a qubit using semiconductor quantum dots. One exploits the valley degree of freedom of conduction electrons in silicon. While these valley states are usually seen as obstacles to spin encoding schemes, we demonstrate the ability to encode a qubit within them. This valley qubit comes with the advantage of sub-nanosecond operation times and protection from charge noise during operation. We further characterize this qubit using quantum process tomography to find fidelities ranging from $79\%-93\%$. The second approach leverages the spin states of holes in a germanium double quantum dot. This area of research has grown rapidly over the past few years, partially because the strong spin-orbit coupling and site-dependent $g$-tensors of these holes allows for all-electrical control of the qubit states without the need for micromagnets. I will characterize the evolution between singlet and triplet states and describe how the hole $g$-tensors can be modified, which are vital to qubit manipulation. By adjusting the voltage applied to the barrier separating the two quantum dots, we have found a $g$-factor that can be increased by approximately an order of magnitude, revealing a sensitivity and tunability these $g$-tensors have to the the local electrostatic environment.

Download or read book Development and Application of Semiconductor Quantum Dots to Quantum Computing written by and published by . This book was released on 2002 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work focuses on developing and applying the necessary methodology for the understanding and application of semiconductor quantum dots for quantum computing. Several major milestones were achieved during the present program including the demonstration of optically induced and detected quantum entanglement of two qubits, Rabi oscillation (one bit rotation) in single q-bit, and demonstration of the two-bit system. Future work is focusing on demonstrating a scalable system as well as working to developing lived coherent states based on optically driven spin systems.

Download or read book Qubit Readout with the Josephson Photomultiplier written by and published by . This book was released on 2016 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent demonstrations of error correction in many qubit circuits, as well as efforts to build a logical qubit, have shown the need for a simple and scalable superconducting quantum bit (qubit) readout. Current solutions based on heterodyne detection and cryogenic amplification of microwave readout tones may prove difficult to scale, while photon counting presents an attractive alternative. However, the development of counters operating at these frequencies has proved technically challenging. In this thesis, we describe the development of the Josephson Photomultipler (JPM), a microwave photon counting circuit. We discuss the JPM theoretically, and describe the fabrication of the JPM using standard thin film lithography techniques. We measure its properties as a microwave photon counter using a qubit as an in-situ calibrated source of photons. We measure a JPM quantum efficiency at the few percent level. We then use the JPM to perform readout of a transmon qubit in both the dispersive and bright regimes. We observe raw measurement fidelities of 35% and 62% respectively. We discuss how the JPM and measurement protocol could be further optimized to achieve fidelities in excess of 90%.

Download or read book Single Atom Nanoelectronics written by Enrico Prati and published by CRC Press. This book was released on 2016-04-19 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: Single-Atom Nanoelectronics covers the fabrication of single-atom devices and related technology, as well as the relevant electronic equipment and the intriguing new phenomena related to single-atom and single-electron effects in quantum devices. It also covers the alternative approaches related to both silicon- and carbon-based technologies, also

Download or read book Manipulating Quantum Systems written by National Academies of Sciences, Engineering, and Medicine and published by National Academies Press. This book was released on 2020-09-14 with total page 315 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of atomic, molecular, and optical (AMO) science underpins many technologies and continues to progress at an exciting pace for both scientific discoveries and technological innovations. AMO physics studies the fundamental building blocks of functioning matter to help advance the understanding of the universe. It is a foundational discipline within the physical sciences, relating to atoms and their constituents, to molecules, and to light at the quantum level. AMO physics combines fundamental research with practical application, coupling fundamental scientific discovery to rapidly evolving technological advances, innovation and commercialization. Due to the wide-reaching intellectual, societal, and economical impact of AMO, it is important to review recent advances and future opportunities in AMO physics. Manipulating Quantum Systems: An Assessment of Atomic, Molecular, and Optical Physics in the United States assesses opportunities in AMO science and technology over the coming decade. Key topics in this report include tools made of light; emerging phenomena from few- to many-body systems; the foundations of quantum information science and technologies; quantum dynamics in the time and frequency domains; precision and the nature of the universe, and the broader impact of AMO science.

Download or read book Spin orbit Coupling Effects in Two Dimensional Electron and Hole Systems written by Roland Winkler and published by Springer Science & Business Media. This book was released on 2003-10-10 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first part provides a general introduction to the electronic structure of quasi-two-dimensional systems with a particular focus on group-theoretical methods. The main part of the monograph is devoted to spin-orbit coupling phenomena at zero and nonzero magnetic fields. Throughout the book, the main focus is on a thorough discussion of the physical ideas and a detailed interpretation of the results. Accurate numerical calculations are complemented by simple and transparent analytical models that capture the important physics.