Controlling Photons, Qubits and their Interactions in Superconducting Electronic Circuits

Rex Lundgren, Neereja Sundaresan, Guanyu Zhu +2 more

Wei Feng, Da‐Wei Wang

We propose the generation of effective three-body interactions in superconducting circuits by coupling qubits or resonators to a bus qubit. Such interactions are characterized by energy exchange between two qubits or resonators depending on the state of the bus qubit. We show that a controlled-iswap (-$\sqrt{\mathrm{i}swap}$) gate can be naturally implemented based on the three-body interactions and it can be used to construct a quantum Fredkin (controlled-swap) gate. A generalized Fredkin gate which controls the swapping of photons between two resonators can be realized in a similar way. It can be used to generate the entangled state of a high number of photons. This proposal is promising to be demonstrated with superconducting circuits previously reported and will stimulate the implementation of multiqubit quantum gates based on many-body interactions.

Philip Jones

Superconducting quantum bits are one of the leading frontrunners in the race to build a solid-state quantum computer. In circuit quantum electrodynamics (cQED), electronic quantum circuits, playing the role of quantum bits, qubits, are placed into superconducting cavities with incredibly weak dissipation. The resulting system exhibits both photon and qubit characteristics, and it is possible to perform complex operations by driving the system with microwaves. Progress has been rapid, with vast improvements in cavities, qubits, and in controlling the interaction between the two. As a result, the first simple quantum algorithms to utilize this architecture have recently been implemented. \nAt the same time, there have been significant developments in improving our understanding of the heat flow in nanoelectronics. In particular the development of tunnel junctions has reached such a level, that it is now possible to control and measure the temperature of small metal islands with high precision. Such techniques have enabled the first observations of quantum-limited heat conduction through the photonic modes of a circuit. \nThis thesis introduces some of the benefits that come with the unification of these two fields. Theoretical models for experiments in a superconducting cavity are presented, with heat conduction due to individual cavity photons discussed in detail, along with a novel method to vary the lifetime of a qubit over many orders of magnitude. The realisation of these experiments would be the first steps on the road to integrating normal-metal components with cQED.

Shreya, Bhawna, Sukhvir Singh +1 more

Nobuyuki Yoshikawa

The recent rapid increase in the scale of superconducting quantum computing systems greatly increases the demand for qubit control by digital circuits operating at qubit temperatures. In this paper, superconducting digital circuits, such as single-flux quantum and adiabatic quantum flux parametron circuits are described, that are promising candidates for this purpose. After estimating their energy consumption and speed, a conceptual overview of the superconducting electronics for controlling a multiple-qubit system is provided, as well as some of its component circuits.

Irfan A. Siddiqi