Detection of Majorana Fermions in circuit QED

Sheng Liu, Chuan-Jia Shan, Zhi-Ming Zhang +1 more

Yasaman Bahri, Ashvin Vishwanath

Daniel B. Szombati, Jeremy Stevens, Nathanaël Cottet +9 more

Clemens Müller, Jérôme Bourassa, Alexandre Blais

Motivated by recent experimental progress towards the measurement and manipulation of Majorana fermions with superconducting circuits, we propose a device interfacing Majorana fermions with circuit quantum electrodynamics. The proposed circuit acts as a charge parity detector changing the resonance frequency of a superconducting $\ensuremath{\lambda}/4$ resonator conditioned on the parity of charges on nearby gates. Operating at both charge and flux sweet spots, this device is highly insensitive to environmental noise. It enables high-fidelity single-shot quantum nondemolition readout of the state of a pair of Majorana fermions encoding a topologically protected qubit. Additionally, the interaction permits the realization of an arbitrary phase gate on the topological qubit, closing the loop for computational completeness. Away from the charge sweet spot, this device can be used as a highly sensitive charge detector with a sensitivity better than ${10}^{\ensuremath{-}4}\text{e}/\sqrt{\text{Hz}}$ and bandwidth larger than 1 MHz.

Oscar Erlandsson

Theoretical understanding indicates that Majorana zero modes in solid-state systems could be utilized for fault-tolerant quantum information processing. The ability to reliably detect these excitations, however, remains a challenge and many of their properties are still unknown. In this Master's project, devices that implement a circuit quantum electrodynamics architecture and are predicted to host Majorana zero modes have been fabricated and characterized at temperatures below 50 mK. Single-junction as well as split-junction geometries have been investigated. In neither case have the expected Majorana signatures been detected. A primary difficulty is operating the devices in magnetic fields large enough to induce the presence of Majorana zero modes. Effects in which the signatures are expected to occur, charge dispersion for the single-junction case and flux dependence for the split-junction case, have been resolved at in-plane fields of approximately 150 mT and 300 mT, respectively. Although non-affirmative of the existence of Majorana states in the devices, the results represent a step toward detection and eventually utilization of Majorana zero modes in superconducting circuits.

Dirk K. Morr