Abstract
We report measurements made at millikelvin temperatures of a superconducting coplanar waveguide resonator (CPWR) coupled to a sphere of yttrium-iron garnet. Systems hybridising collective spin excitations with microwave photons have recently attracted interest for their potential quantum information applications. In this experiment the non-uniform microwave field of the CPWR allows coupling to be achieved to many different magnon modes in the sphere. Calculations of the relative coupling strength of different mode families in the sphere to the CPWR are used to successfully identify the magnon modes and their frequencies. The measurements are extended to the quantum limit by reducing the drive power until, on average, less than one photon is present in the CPWR. Investigating the time-dependent response of the system to square pulses, oscillations in the output signal at the mode splitting frequency are observed. These results demonstrate the feasibility of future experiments combining magnonic elements with planar superconducting quantum devices.
Highlights
Magnons are elementary excitations of magnetically ordered materials
In this paper we investigate the coupling of magnons in a Yttrium-iron garnet (YIG) sphere to photons in a coplanar waveguide resonator (CPWR)
This work validates our understanding of the behaviour and interactions of magnon systems at millikelvin temperatures, and is a necessary step in the development of experimental systems coupling magnons to 2D circuit quantum electrodynamic systems
Summary
Magnons are elementary excitations of magnetically ordered materials. For more than half a century, their study has been recognized as a fertile area of research; both for its rich fundamental physics, and its potential technological applications. Yttrium-iron garnet (YIG) is a ferrimagnetic garnet with extremely low magnon damping[3] This low loss, in combination with very low electrical conductivity, makes it ideal for the production of high-Q microwave resonators and waveguides. The use of such systems in the development of devices for quantum computation has begun to attract significant attention[7]. This has led to a number of investigations into architectures for coupling magnons to photons in ways that can be extended into the quantum regime, in the new field of quantum magnonics. As well as opening up the possibility for novel hybrid devices incorporating magnonic systems, coupling such structures to YIG would offer new tools to study the quantum physics of magnons. This work validates our understanding of the behaviour and interactions of magnon systems at millikelvin temperatures, and is a necessary step in the development of experimental systems coupling magnons to 2D circuit quantum electrodynamic (cQED) systems
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