Fundamental Limits of Self-localization for Cooperative Robotic Platforms Using Signals of Opportunity

Abstract The positioning technique employing the ubiquitous signals of opportunity of non-cooperative satellites does not send special navigation signals, instead it passively receives satellite signals as noise, presenting advantages of concealment and difficulty for potential attackers. Thus, this study investigates the ranging principle and model using non-cooperative communication satellites and a time difference estimation algorithm. The technology of time difference measurement under non-cooperative observation mode was determined and simulated. A test platform for time difference measurement was built to receive the signal from an unknown geostationary Earth orbit communication satellite and verify the ranging feasibility and performance. The ranging accuracy was found to be smaller than 6 m, as demonstrated by experimental data, which shows the viability of the proposed positioning technique for ranging technology.

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Fundamental limits of electron and nuclear spin qubit lifetimes in an isolated self-assembled quantum dot

npj Quantum Information ◽

10.1038/s41534-021-00378-2 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

George Gillard ◽

Ian M. Griffiths ◽

Gautham Ragunathan ◽

Ata Ulhaq ◽

Callum McEwan ◽

...

Keyword(s):

Quantum Dot ◽

Spin Relaxation ◽

Nuclear Spin ◽

Operating Conditions ◽

External Control ◽

Spin Qubits ◽

Fundamental Limits ◽

Trade Offs ◽

Wide Range ◽

Spin Qubit

AbstractCombining external control with long spin lifetime and coherence is a key challenge for solid state spin qubits. Tunnel coupling with electron Fermi reservoir provides robust charge state control in semiconductor quantum dots, but results in undesired relaxation of electron and nuclear spins through mechanisms that lack complete understanding. Here, we unravel the contributions of tunnelling-assisted and phonon-assisted spin relaxation mechanisms by systematically adjusting the tunnelling coupling in a wide range, including the limit of an isolated quantum dot. These experiments reveal fundamental limits and trade-offs of quantum dot spin dynamics: while reduced tunnelling can be used to achieve electron spin qubit lifetimes exceeding 1 s, the optical spin initialisation fidelity is reduced below 80%, limited by Auger recombination. Comprehensive understanding of electron-nuclear spin relaxation attained here provides a roadmap for design of the optimal operating conditions in quantum dot spin qubits.

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