High-Temperature Single-Electron Transistors Based on Molecules and Small Nanoparticles.

The material of the defense of the dissertation for the degree of Doctor of Physical and Mathematical Sciences – the first in Russia doctoral dissertation on molecular singe-electronics is presented. The relevance of the development, creation and research of single-electron transistorswith high charge energy and operating temperature for the creation of fundamentally new nanoelectronic devices applicable in wide practice and ensuring breakthrough research in various fields is noted, the necessity of using quantum dots (molecules/nanoparticles) of atomic-molecular scale for this is shown, the formulation of the research problems is formulated, the physical and technological methods of fabrication and analysis used are listed, the main results of the work are presented and their significance for the development of highly sensitive sensing, quantum informatics and quantum metrology is discussed.

Experimental critical quantum metrology with the Heisenberg scaling

Critical quantum metrology, which exploits quantum critical systems as probes to estimate a physical parameter, has gained increasing attention recently. However, the critical quantum metrology with a continuous quantum phase transition (QPT) is experimentally challenging since a continuous QPT only occurs at the thermodynamic limit. Here, we propose an adiabatic scheme on a perturbed Ising spin model with a first-order QPT. By introducing a small transverse magnetic field, we can not only encode an unknown parameter in the ground state but also tune the energy gap to control the evolution time of the adiabatic passage. Moreover, we experimentally implement the critical quantum metrology scheme using nuclear magnetic resonance techniques and show that at the critical point the precision achieves the Heisenberg scaling as 1/T. As a theoretical proposal and experimental implementation of the adiabatic scheme of critical quantum metrology and its advantages of easy implementation, inherent robustness against decays and tunable energy gap, our adiabatic scheme is promising for exploring potential applications of critical quantum metrology on various physical systems.

Dynamic synthesis of Heisenberg-limited spin squeezing

Spin squeezing is a key resource in quantum metrology, allowing improvements of measurement signal-to-noise ratio. Its generation is a challenging task because the experimental realization of the required squeezing interaction remains difficult. Here, we propose a generic scheme to synthesize spin squeezing in non-squeezing systems. By using periodical rotation pulses, the original non-squeezing interaction can be transformed into squeezing interaction, with significantly enhanced interaction strength. The sign of the interaction coefficient is also flippable, facilitating time-reversal readout protocol for nonlinear interferometers. The generated spin squeezing is capable of achieving the Heisenberg limit with measurement precision ∝ 1/N for N particles and its robustness to noises of pulse areas and separations has been verified as well. This work offers a path to extending the scope of Heisenberg-limited quantum precision measurements in non-squeezing systems.

Simple representation of the quantum entanglement of coupled harmonic oscillators in terms of the reflection coefficient

Quantum entanglement of coupled harmonic oscillators is frequently applied in quantum and non-linear physics, molecular chemistry and biophysics, which is why its study is of a great interest for modern physics. In this work a quantum entanglement of a coupled harmonic oscillator in a simple form was found. This simple form is presented as a single parameter – reflection coefficient R. All parameters of the studied system are included in the R coefficient. It is shown that the derivation of the expression can have applications in quantum optics, in particular in quantum metrology.