Francesco Cioni

The Haldane model represents the minimal lattice-based realization of a Chern insulator, exhibiting a quantized Hall conductance in the absence of Landau levels. Despite its conceptual elegance, the implementation in crystalline solids of the requisite pattern of Peierls phases breaking time-reversal symmetry remains experimentally demanding. In this work, we theoretically investigate the possibility to simulate the Haldane model in ultraclean GaAs/AlGaAs heterostructures. Our proposal relies on recent experiments in which a high-mobility two-dimensional electron gas is subject to a gate-defined honeycomb electrostatic potential and a laterally periodic magnetic field generated by patterned ferromagnetic structures. The combined electrostatic and magnetic superlattices furnish a viable route to emulate the topological properties of the Haldane model.

The processing unit of a solid-state quantum computer consists of an array of coupled qubits, each driven with on-chip microwave lines that route control signals to the qubits in order to perform logical operations. This approach to quantum computing comes with two major problems. On the one hand, it greatly hampers scalability towards fault-tolerant quantum computers, which are estimated to need a number of qubits—and therefore driving lines—on the order of 10 6 . On the other hand, these lines are a source of electromagnetic noise, exacerbating frequency crowding and crosstalk, while also contributing to power dissipation inside the dilution fridge. We here tackle these two challenges by presenting a quantum processing unit (QPU) for a universal quantum computer which is (rather than ) driven. Our QPU relies on a closed loop of superconducting qubits with always-on ZZ interactions which we dub the “conveyor belt.” Notably, this architecture requires only O ( N ) physical qubits to run a computation on N computational qubits, in contrast to previous O ( N 2 ) proposals for global quantum computation. Universality is achieved via the implementation of single-qubit gates and a Toffoli gate. The ability to perform multiqubit operations in a single step could vastly improve the fidelity and execution time of many algorithms.

We propose a platform for implementing a universal, quantum computer based on a 2D ladder hosting three different species of superconducting qubits. In stark contrast with the existing literature, our scheme exploits the always-on longitudinal ZZ coupling. The latter, combined with specific driving frequencies, enables the reach of a blockade regime, which plays a pivotal role in the computing scheme.