Abstract
Analog quantum simulations offer rich opportunities for exploring complex quantum systems and phenomena through the use of specially engineered, well-controlled quantum systems. A critical element, increasing the scope and flexibility of such experimental platforms, is the ability to access and tune in situ different interaction regimes. Here, we present a superconducting circuit building block of two highly coherent transmons featuring in situ tuneable photon hopping and nonlinear cross-Kerr couplings. The interactions are mediated via a nonlinear coupler, consisting of a large capacitor in parallel with a tuneable superconducting quantum interference device (SQUID). We demonstrate the working principle by experimentally characterising the system in the single-excitation and two-excitation manifolds, and derive a full theoretical model that accurately describes our measurements. Both qubits have high coherence properties, with typical relaxation times in the range of 15 to 40 μs at all bias points of the coupler. Our device could be used as a scalable building block in analog quantum simulators of extended Bose-Hubbard and Heisenberg XXZ models, and may also have applications in quantum computing such as realising fast two-qubit gates and perfect state transfer protocols.
Highlights
Analog quantum simulations, where engineered systems emulate the behaviour of other, less accessible quantum systems in a controllable and measurable way,[1] show significant promise for improving our understanding of complex quantum phenomena without the need for a full fault-tolerant quantum computer.[2,3,4,5] In this paradigm, the versatility of the simulator is determined by the range of interaction types and complexity accessible to the emulating quantum system
Our device could be used as a scalable building block in analog quantum simulators of extended Bose-Hubbard and Heisenberg XXZ models, and may have applications in quantum computing such as realising fast two-qubit gates and perfect state transfer protocols
Superconducting circuit quantum electrodynamics (QED) is a very attractive platform for analog quantum simulation because of sitespecific control and readout, and because of the flexible and engineerable system designs, which have led to the study of many interesting effects.[11,12,13,14,15,16,17,18,19,20,21,22]
Summary
Analog quantum simulations, where engineered systems emulate the behaviour of other, less accessible quantum systems in a controllable and measurable way,[1] show significant promise for improving our understanding of complex quantum phenomena without the need for a full fault-tolerant quantum computer.[2,3,4,5] In this paradigm, the versatility of the simulator is determined by the range of interaction types and complexity accessible to the emulating quantum system. Promising avenues for pushing beyond what can be simulated with a classical machine include the study of highly interacting many-body systems.[6,7,8,9,10] Superconducting circuit quantum electrodynamics (QED) is a very attractive platform for analog quantum simulation because of sitespecific control and readout, and because of the flexible and engineerable system designs, which have led to the study of many interesting effects.[11,12,13,14,15,16,17,18,19,20,21,22] Adding new components to the circuit QED design toolbox such as novel types of interactions can dramatically increase the range of phenomena that can be simulated.[23,24,25] For example, for exploring exotic effects, like quantum phase transitions in systems of strongly correlated particles, it is important to be able to access and rapidly tune between different many-body interaction regimes
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