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arXiv:1509.01619 · Physical Review Applied

Planar Multilayer Circuit Quantum Electrodynamics

Zlatko Minev, Kyle Serniak, Ioan M. Pop, Zaki Leghtas, K. Sliwa, M. Hatridge, Luigi Frunzio, R. J. Schoelkopf, Michel Devoret

Published Apr 29, 2016• 38 citations
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Abstract

Circuit quantum electrodynamics promises an efficient realization of the quantum computer, but what should the architecture be? The authors demonstrate a system that successfully marries the advantages of two approaches: the integration capacity of a two-dimensional (planar) layout, plus the high quantum coherence of a three-dimensional structure. This approach is practical for a range of applications, including hybrid systems incorporating semiconducting nanostructures or trapped atoms.

DOI
10.1103/physrevapplied.5.044021

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Circuit quantum electrodynamics promises an efficient realization of the quantum computer, but what should the architecture be? The authors demonstrate a system that successfully marries the advantages of two approaches: the integration capacity of a two-dimensional (planar) layout, plus the high quantum coherence of a three-dimensional structure. This approach is practical for a range of applications, including hybrid systems incorporating semiconducting nanostructures or trapped atoms.
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Numerous loss mechanisms can limit coherence and scalability of planar and 3D-based circuit quantum electrodynamics (cQED) devices, particularly due to their packaging. The low loss and natural isolation of 3D enclosures make them good candidates for coherent scaling. We introduce a coaxial transmission line device architecture with coherence similar to traditional 3D cQED systems. Measurements demonstrate well-controlled external and on-chip couplings, a spectrum absent of cross-talk or spurious modes, and excellent resonator and qubit lifetimes. We integrate a resonator-qubit system in this architecture with a seamless 3D cavity, and separately pattern a qubit, readout resonator, Purcell filter, and high-Q stripline resonator on a single chip. Device coherence and its ease of integration make this a promising tool for complex experiments.
The next step in building quantum computers is to develop hardware architectures that allow scalability without sacrificing coherence. Future designs seem headed toward multilayered circuits with embedded three-dimensional structures and superconducting coatings. The authors demonstrate a multilayered integrated quantum circuit, combining a micromachined microwave cavity resonator with a superconducting qubit. They address the mechanism of coupling and its control, engineering considerations that affect coherence times, and challenges in fabrication such as superconductor bonding.
High-dimensional quantum systems, known as qudits with dimension d>2d>2d>2, possess the capability to encode and process more information than traditional two-dimensional qubits. Entangled states serve as crucial resources for both quantum computation and quantum communication. On the basis of circuit quantum electrodynamics (QED) systems, we introduce an efficient scheme to deterministically generate high-dimensional multipartite entangled states of hybrid qutrits (d=3d=3d=3). Assuming a simple initial state has already been prepared with the use of local operations, our method requires only a single step to produce hybrid Greenberger-Horne-Zeilinger (GHZ) entangled states among circuit QED systems consisting of superconducting qutrits and a superconducting cavity. Remarkably, the number of steps and the operational time remain constant as the number of qutrits increases, highlighting the efficiency and scalability of our approach. Using numerical simulations for a three-dimensional hybrid GHZ state of seven qutrits, we demonstrate the feasibility of our scheme and study the effects of various parameters on the fidelity. The importance of this research is in directing the experimental creation of multipartite, high-dimensional, and hybrid GHZ states, which can then be used to enhance quantum communication protocols and computational processes.
The present review attempts to sum up the advancements in circuit quantum electrodynamics (CQED) that has raised our hope for realizing scalable quantum information processing (QIP). Research reveals the advantages of (QIP) over classical information processing in terms of information storage capacity and speed of processing. In this context, the mathematical framework for QIP, like Quantum Fisher Information and computations based on Hilbert space is reviewed. CQED architectures of ever improving configuration are being reported in technical literature. Further, improvements are noticed in coupling strengths between the qubit and the resonator by application of robust protocols. The review highlights the Research efforts and the advancements achieved through faithful quantum state transfer between spatially separated qubits. The important phenomenon of entanglement, deterministic and multipartite, as the cornerstone for scalable QIP is discussed to bring forth the advancements achieved in reducing decoherence and decay. The author sums up the review with a discussion of selected patents and commercial endeavours in the field.
Qubit shuttling has become an indispensable ingredient for scaling leading quantum computing platforms, including semiconductor spin, neutral-atom, and trapped-ion qubits, enabling both crosstalk reduction and tighter integration of control hardware. Cai et al. (2023) proposed a scalable architecture that employs short-range shuttling to realize effective three-dimensional connectivity on a strictly two-dimensional device. Building on recent advances in quantum error correction, we show that this architecture enables the native implementation of folded surface codes on 2D hardware, reducing the runtime of all single-qubit logical Clifford gates and logical CNOTs within subsets of qubits from O(d)\mathcal{O}(d)O(d) in conventional surface code lattice surgery to constant time. We present explicit protocols for these operations and demonstrate that access to a transversal SSS gate reduces the spacetime volume of 8T-to-CCZ magic-state distillation by more than an order of magnitude compared with standard 2D lattice surgery approaches. Finally, we introduce a new "virtual-stack" layout that more efficiently exploits the quasi-three-dimensional structure of the architecture, enabling efficient multilayer routing on these two-dimensional devices.