We propose a novel platform for quantum many body simulations of dipolar spin models using current circuit QED technology. Our basic building blocks are 3D Transmon qubits where we use the naturally occurring dipolar interactions to realize interacting spin systems. This opens the way toward the realization of a broad class of tunable spin models in both two-and onedimensional geometries. We illustrate the potential offered by these systems in the context of dimerized Majumdar-Ghosh-type phases, archetypical examples of quantum magnetism, showing how such phases are robust against disorder and decoherence, and could be observed within stateof-the-art experiments.PACS numbers: 03.67. Ac, 42.50.Dv, 75.10.Pq Introduction. -In the present work we propose and analyze a novel setup for an analog quantum simulator of quantum magnetism using superconducting qubits. The scheme builds on the remarkable recent developments in Circuit QED [1][2][3][4][5][6] in the context of quantum simulation [7][8][9][10][11], and especially the 3D Transmon qubit [12,13]. The scheme promises a faithful implementation of many-body spin-1/2 Hamiltonians involving tens of qubits using state-of-the-art experimental techniques. The central idea behind the present work is to exploit the naturally occurring dipolar interactions between qubits to engineer the desired spin-spin interactions. In combination with the flexibility offered by solid-state setups for realizing arbitrary geometry arrangements, this allows us to design general dipolar spin models in ladder and 2D geometries. As we will show, our scheme competes favorably with present and envisaged quantum simulation setups for magnetism with cold atoms and trapped ions [14][15][16], and enables us to address some of the key challenges of quantum simulation including equilibrium and non-equilibrium (quench) dynamics [17]. Moreover, we note that exploiting dipolar interactions to design dipolar spin models is conceptually different, and complementary to the remarkable recent experiments with superconducting circuits toward realizing the superfluid-Mott insulator transition, based on wiring up increasingly complex circuits of superconducting stripline cavities [7].In our analysis we address two of the key aspects of the design of our proposed simulator for quantum magnetism. First, we present a feasibility study of state-ofthe-art experimental setups: this includes a discussion of the general mechanism to generate dipolar interactions between 3D Transmons, combined with ab initio simulations of the coupling strength in our spin model for various geometries. Second, we illustrate how state-ofthe-art setups, composed of up to a dozen qubits and characterized by typical disorder and decoherence rates, are already able to demonstrate paradigmatic signatures of quantum magnetism. In particular, we show how a dimerized phase [18], a valence-bond-solid reminiscent of the Majumdar-Ghosh state widely discussed in the context of quantum spin chains [19], can be realized and probed with current techn...
We present an experimental investigation of stochastic switching of a bistable Josephson junctions array resonator with a resonance frequency in the GHz range. As the device is in the regime where the anharmonicity is on the order of the linewidth, the bistability appears for a pump strength of only a few photons. We measure the dynamics of the bistability by continuously observing the jumps between the two metastable states, which occur with a rate ranging from a few Hz down to a few mHz. The switching rate strongly depends on the pump strength, readout strength and the temperature, following Kramer's law. The interplay between nonlinearity and coupling, in this little explored regime, could provide a new resource for nondemolition measurements, single photon switches or even elements for autonomous quantum error correction.The non-linearity provided by atoms and Josephson junctions is a necessary ingredient to observe quantum mechanical effects in cavity quantum-electro-dynamics (QED) and circuit QED (cQED) systems. Strong nonlinearites, much larger than the linewidth of the transition, are required to realize qubits 1 , implement quantum information protocols 2,3 and realize textbook quantum optics experiments 4,5 . Non-linearities much smaller than the linewidth of the transition are typically exploited for parametric processes 6-8 like amplification or frequency conversion at the quantum level.Besides quantum information applications, there has been a growing interest to exploit cavity QED for ultralow-power classical logic elements 9-11 . This interest has been sparked by the ever growing all optical communication networks. Remarkably, a single photon transistor 12 , reminiscent of an electronic transistor, has been implemented for the optical domain. In this device a single photon can switch a large optical field. Realizing such devices has been a challenging endeavour as the required non-linearity is hard to realize, due to the weak interaction of optical light with atoms.Much stronger light matter interactions can be achieved in the microwave regime using the cQED platform. In this context Josephson junction arrays (JJAs) have proven to be an ideal circuit element to build superconducting qubits with excellent coherence properties and unique tuning capabilities [13][14][15] . Similarly, JJAs have also been used to build quantum limited parametric amplifiers 8,[16][17][18] . Recently, the coherence properties of the self resonances of JJAs 19,20 , as well as their self-Kerr and cross-Kerr coefficients have been measured 21 . The measured Kerr coefficient showed good agreement with a model based on a second order expansion of the Josephson potential 22 . A regime of particular interest arises when the selfKerr K i and cross-Kerr K ij nonlinear coefficients are on the order of the linewidth κ of the system. In this regime the system will show a pronounced bistability 23,24 at the single to few photon level. Bistability is a phenomenon which is relevant in many fields, ranging from chemistry 25 and biology ...
Here we present the microwave characterization of microstrip resonators made from aluminum and niobium inside a 3D microwave waveguide. In the low temperature, low power limit internal quality factors of up to one million were reached. We found a good agreement to models predicting conductive losses and losses to two level systems for increasing temperature. The setup presented here is appealing for testing materials and structures, as it is free of wire bonds and offers a well controlled microwave environment. In combination with transmon qubits, these resonators serve as a building block for a novel circuit QED architecture inside a rectangular waveguide.Microwave resonators are an important building block for circuit QED systems where they are e.g. used for qubit readout 1,2 , to mediate coupling 3 and for parametric amplifiers 4 . All of these applications require low intrinsic losses at low temperatures (k B T hf r ) and at single photon drive strength. In this low energy regime, the intrinsic quality factor, which quantifies internal losses, is often limited by dissipation due to two level systems (TLS) 5,6 . These defects exist mainly in metal-air, metalsubstrate and substrate-air interfaces as well as in bulk dielectrics 6-9 . Two common approaches exist, to improve the intrinsic quality factor of resonators. Either one reduces the sensitivity to these loss mechanisms by reducing the participation ratio 6,10,11 or tries to improve the interfaces by a sophisticated fabrication process 12,13 . Reducing the participation ratio requires to reduce the electric field strength. This is typically done by increasing the size of the resonator 8 or even implementing the resonator using three dimensional structures 10 .Our approach, a microstrip resonator (MSR) in a rectangular waveguide (Fig. 1), combines the advantages of three dimensional structures with a compact, planar design 2,14 . The sensitivity to interfaces is reduced, since the majority of the field is spread out over the waveguide, effectively reducing the participation ratio 11 . Another advantage is, that the waveguide represents a clean and well controlled microwave environment 15 without lossyseams 16 close to the MSR. As the MSR is capacitively coupled to the waveguide, no wirebonds 17 or airbridges 18 are required, which can lead to dissipation or crosstalk.The U-shaped MSR ( Fig.
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