Protected qubits based on superconducting circuit topology

Phillipe Campagne-Ibarcq, Mazyar Mirrahimi, Michel Devoret

Sergey P. Gladchenko, David Olaya, Eva Dupont-Ferrier +3 more

Pablo Perez-Fernandez, Manuel Pino

We show that topological edge states can be realized in a simple superconducting circuit composed of an inductively shunted flux qubit. The Josephson potential of that qubit forms a honeycomb lattice similar to the case of graphene. The additional shunting element produces a quartic potential along one flux direction, which effectively creates a boundary in flux space. We map analytically the low-energy dynamics of the circuit to an extended Su--Schrieffer--Heeger (SSH) chain, in which a quartic potential is added to the usual SSH Hamiltonian. This mapping is confirmed by numerical simulations of the full superconducting circuit. We argue that chiral symmetry still holds for the edge states of the extended model around a chiral point in parameter space. Close to this point, we numerically find that edge states in our superconducting circuit are topologically protected against perturbations that obey chiral symmetry, as is the case for charge noise. Our results show that topological effects previously thought to occur in multi-qubit systems, such as protection against decoherence, can also be found in much simpler single superconducting qubits.

Lin Tian

Robust quantum state transfer (QST) is an indispensable ingredient in scalable quantum information processing. Here we present an experimentally feasible scheme for robust QST via topologically protected edge states in superconducting circuits. Using superconducting X-mon qubits with tunable couplings, the generalized Su-Schrieffer-Heeger models with topological magnon bands can be constructed. A novel entanglement-dependent topological Thouless pumping can be directly observed in this system. More importantly, we show that single-qubit states and entanglement can be robustly transferred with high fidelity in the presence of qubit-coupling imperfection, which is a hallmark of topological protection. This approach is experimentally applicable to a variety of quantum systems.

Chaohua Wu, Xin Guan, Jingtao Fan +2 more

The recent experimental realization of a programmable two-dimensional square superconducting qubit array opens a new avenue for quantum simulation with qubits [Science 372, 948 (2021)]. Here, we present an experimentally feasible method to achieve two-dimensional superconducting qubit lattice with tunable coupling strengths. A configuration with higher-order topological phases is constructed, featuring topologically protected boundary states in lower dimension (corner states). We show that the quadrupole topological phases can be effectively characterized by the dynamics of the single-excitation quantum state. Moreover, we also explore the detection and dynamics of the corner modes in our qubit lattice system. Particularly, we propose an effective scheme to realize quantum information transfer via the corner states. Our work suggests that superconducting circuits systems are a fertile platform to study novel topological quantum phases and may shed light on the ongoing exploration of topologically protected quantum information processing.

Shreya, Bhawna, Sukhvir Singh +1 more