Hybrid quantum circuits: Superconducting circuits interacting with other quantum systems (original) (raw)
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Hybrid Quantum Circuit with a Superconducting Qubit Coupled to a Spin Ensemble
Physical Review Letters, 2011
Present-day implementations of quantum information processing rely on two widely different types of quantum bits (qubits). On the one hand, microscopic systems such as atoms or spins are naturally well decoupled from their environment and as such can reach extremely long coherence times ; on the other hand, more macroscopic objects such as superconducting circuits are strongly coupled to electromagnetic fields, making them easy to entangle although with shorter coherence times . It thus seems appealing to combine the two types of systems in hybrid structures that could possibly take the best of both worlds. Here we report the first experimental realization of a hybrid quantum circuit in which a superconducting qubit of the transmon type is coherently coupled to a spin ensemble consisting of nitrogen-vacancy (NV) centers in a diamond crystal [8] via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare arbitrary superpositions of the qubit states that we store into collective excitations of the spin ensemble and retrieve back later on into the qubit. We demonstrate that this process preserves quantum coherence by performing quantum state tomography of the qubit. These results constitute a first proof of concept of spin-ensemble based quantum memory for superconducting qubits [12]. As a landmark of the successful marriage between a superconducting qubit and electronic spins, we detect with the qubit the hyperfine structure of the NV center.
Quantum technologies with hybrid systems
Proceedings of the National Academy of Sciences, 2015
An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near-and long-term perspectives of this fascinating and rapidly expanding field.
Superconducting circuits and quantum information
Superconducting circuits can behave like atoms making transitions between two levels. Such circuits can test quantum mechanics at macroscopic scales and be used to conduct atomic-physics experiments on a silicon chip.
Superconducting circuits and quantum computation
Quantum computers are devices that store information on quantum variables such as spin, photons, and atoms, and process that information by making those variables interact in a way that preserves quantum coherence. Typically, these variables consist of two-state quantum systems called quantum bits or 'qubits'. To perform a quantum computation, one must be able to prepare qubits in a desired initial state, coherently manipulate superpositions of a qubit's two states, couple qubits together, measure their state, and keep them relatively free from interactions that induce noise and decoherence.
Controlling quantum information processing in hybrid systems on chips
Quantum Information Processing, 2011
We investigate quantum information processing, transfer and storage in hybrid systems comprised of diverse blocks integrated on chips. Strong coupling between superconducting (SC) qubits and ensembles of ultracold atoms or NV-center spins is mediated by a microwave transmission-line resonator that interacts near-resonantly with the atoms or spins. Such hybrid devices allow us to benefit from the advantages of each block and compensate for their disadvantages. Specifically, the SC qubits can rapidly implement quantum logic gates, but are "noisy" (prone to decoherence), while collective states of the atomic or spin ensemble are "quiet"(protected from decoherence) and thus can be employed for storage of quantum information. To improve the overall performance (fidelity) of such devices we discuss dynamical control to optimize quantum state-transfer from a "noisy" qubit to the "quiet" storage ensemble. We propose to maximize the fidelity of transfer and storage in a spectrally inhomogeneous spin ensemble, by pre-selecting the optimal spectral portion of the ensemble. Significant improvements of the overall fidelity of hybrid devices are expected under realistic conditions. Experimental progress towards the realization of these schemes is discussed.
Superconducting Circuits for Quantum Information: An Outlook
Science, 2013
The performance of superconducting qubits has improved by several orders of magnitude in the past decade. These circuits benefit from the robustness of superconductivity and the Josephson effect, and at present they have not encountered any hard physical limits. However, building an error-corrected information processor with many such qubits will require solving specific architecture problems that constitute a new field of research. For the first time, physicists will have to master quantum error correction to design and operate complex active systems that are dissipative in nature, yet remain coherent indefinitely. We offer a view on some directions for the field and speculate on its future.
Physical Review A, 2005
We describe the design for a scalable, solid-state quantum-information-processing architecture based on the integration of GHz-frequency nanomechanical resonators with Josephson tunnel junctions, which has the potential for demonstrating a variety of single-and multiqubit operations critical to quantum computation. The computational qubits are eigenstates of large-area, current-biased Josephson junctions, manipulated and measured using strobed external circuitry. Two or more of these phase qubits are capacitively coupled to a high-quality-factor piezoelectric nanoelectromechanical disk resonator, which forms the backbone of our architecture, and which enables coherent coupling of the qubits. The integrated system is analogous to one or more few-level atoms ͑the Josephson junction qubits͒ in an electromagnetic cavity ͑the nanomechanical reso-nator͒. However, unlike existing approaches using atoms in electromagnetic cavities, here we can individually tune the level spacing of the "atoms" and control their "electromagnetic" interaction strength. We show theoretically that quantum states prepared in a Josephson junction can be passed to the nanomechanical resonator and stored there, and then can be passed back to the original junction or transferred to another with high fidelity. The resonator can also be used to produce maximally entangled Bell states between a pair of Josephson junctions. Many such junction-resonator complexes can be assembled in a hub-and-spoke layout, resulting in a large-scale quantum circuit. Our proposed architecture combines desirable features of both solid-state and cavity quantum electrodynamics approaches, and could make quantum-information processing possible in a scalable, solid-state environment.
Towards quantum electrical circuits
Physica E: Low-dimensional Systems and Nanostructures, 2003
Electrical circuits can behave quantum mechanically when decoherence induced by uncontrolled degrees of freedom is su ciently reduced. Recently, di erent nanofabricated superconducting circuits based on Josephson junctions have achieved a degree of quantum coherence su cient to allow the manipulation of their quantum state with NMR-like techniques. Because of their potential scalability, these quantum circuits are presently considered for implementing quantum bits, which are the building blocks of the proposed quantum processors. We have operated such a Josephson qubit circuit in which a long coherence time is obtained by decoupling the qubit from its readout circuit during manipulation. We report pulsed microwave experiments which demonstrate the controlled manipulation of the qubit state. ?
Recent Progress in Quantum Simulation Using Superconducting Circuits
Journal of Low Temperature Physics, 2014
Quantum systems are notoriously difficult to simulate with classical means. Recently, the idea of using another quantum system-which is experimentally more controllable-as a simulator for the original problem has gained significant momentum. Amongst the experimental platforms studied as quantum simulators, superconducting qubits are one of the most promising, due to relative straightforward scalability, easy design, and integration with standard electronics. Here I review the recent state-of-the art in the field and the prospects for simulating systems ranging from relativistic quantum fields to quantum many-body systems. Keywords Josephson devices • digital and analog quantum simulation • many-body systems • quantum fields • circuit QED Recent progress in quantum simulation using superconducting circuits 3 Recent progress in quantum simulation using superconducting circuits 5