On the VCO/Frequency Divider Interface in Cryogenic CMOS PLL for Quantum Computing Applications

Gabriele Gira,Mattia Borgarino,Elena Ferraro

doi:10.3390/electronics10192404

Abstract

The availability of quantum microprocessors is mandatory, to efficiently run those quantum algorithms promising a radical leap forward in computation capability. Silicon-based nanostructured qubits appear today as a very interesting approach, because of their higher information density, longer coherence times, fast operation gates, and compatibility with the actual CMOS technology. In particular, thanks to their phase noise properties, the actual CMOS RFIC Phase-Locked Loops (PLL) and Phase-Locked Oscillators (PLO) are interesting circuits to synthesize control signals for spintronic qubits. In a quantum microprocessor, these circuits should operate close to the qubits, that is, at cryogenic temperatures. The lack of commercial cryogenic Design Kits (DK) may make the interface between the Voltage Controlled Oscillator (VCO) and the Frequency Divider (FD) a serious issue. Nevertheless, currently this issue has not been systematically addressed in the literature. The aim of the present paper is to investigate the VCO/FD interface when the temperature drops from room to cryogenic. To this purpose, physical models of electronics passive/active devices and equivalent circuits of VCO and the FD were developed at room and cryogenic temperatures. The modeling activity has led to design guidelines for the VCO/FD interface, useful in the absence of cryogenic DKs.

Highlights

Since ancient times, humankind has always been in need of computing; computation capability and knowledge progress have always walked arm in arm
The aim of the present paper is to investigate the frequency mismatch that may arise between the Voltage Controlled Oscillator (VCO) and the Frequency Divider when the temperature drops from room to cryogenic values
VCO and Frequency Divider interface is very critical for a correct operation of the Phase-Locked Loops (PLL), because an excessive frequency mismatch between VCO and frequency may prevent the PLL to reach the lock condition

Summary

Introduction

Humankind has always been in need of computing; computation capability and knowledge progress have always walked arm in arm. In the XXI century a new kind of microprocessor appeared, the quantum microprocessor. It manipulates bits but of a very special type: the quantum bit, or qubit. In order to be efficient, these quantum algorithms should run on a quantum microprocessor where superposition and entanglement are physically available and not emulated, as it may be on a classical microprocessor. This calls for the fabrication of quantum microprocessors. From an engineering point of view, the manipulation of silicon-based qubits requires frequencies that can be synthesized using the actual CMOS Radio Frequency

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Conclusion