Micron-size superconducting quantum interference devices ( $\mu$ -SQUIDs) are highly-sensitive magnetic flux sensors where the critical current or the voltage is modulated by the magnetic flux. The so-called voltage read-out mode is nevertheless often hindered by thermal hysteresis. $\mu$ -SQUIDs with improved thermal evacuation and small critical current can feature a phase-dynamic regime over a narrow bias-current and temperature range. Guided by a dynamic thermal model, we could widen these current and temperature ranges by using a shunt resistor. A significant increase in these ranges and, more strikingly, in the voltage oscillations magnitude is observed when the shunt is made of an adequate inductance in series with the resistor. An increase in inductance above a threshold value leads to relaxation oscillations in voltage. The large voltage modulation thus obtained offers an improved flux resolution in the voltage read-out mode down to 1.3 K.Micron-size superconducting quantum interference devices ($\mu$-SQUIDs) are highly-sensitive magnetic flux sensors where the critical current or the voltage is modulated by the magnetic flux. The so-called voltage read-out mode is nevertheless often hindered by thermal hysteresis. $\mu$-SQUIDs with improved thermal evacuation and small critical current can feature a phase-dynamic regime over a narrow bias-current and temperature range. Guided by a dynamic thermal model, we could widen these current and temperature ranges by using a shunt resistor. A significant increase in these ranges and, more strikingly, in the voltage oscillations magnitude is observed when the shunt is made of an adequate inductance in series with the resistor. An increase in inductance above a threshold value leads to relaxation oscillations in voltage. The large voltage modulation thus obtained offers an improved flux resolution in the voltage read-out mode down to 1.3 K.

Aug 17, 20180 citations

Cooling and heating of a quantum oscillator

A.N Lebedev

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated EquipmentMay 1, 19970 citations

Entanglement dynamics of two coupled mechanical oscillators in modulated optomechanics

Subhadeep Chakraborty, Amarendra K. Sarma

We study the entanglement dynamics of two coupled mechanical oscillators, within a modulated optomechanical system. We find that, depending on the strength of the mechanical coupling, one could observe either a stationary or a dynamical behavior of the mechanical entanglement, which is extremely robust against the oscillator temperature. Moreover, we have shown that this entanglement dynamics is strongly related to the stability of the normal modes. Taking mechanical damping effects into account, an analytical expression corresponding to the critical mechanical coupling strength, where the transition from stationary to dynamical entanglement occurs, is also reported. The proposed scheme is analyzed with experimentally realistic parameters, making it a promising means to realize macroscopic quantum entanglement within current state-of-the-art experimental setups.We study the entanglement dynamics of two coupled mechanical oscillators, within a modulated optomechanical system. We find that, depending on the strength of the mechanical coupling, one could observe either a stationary or a dynamical behavior of the mechanical entanglement, which is extremely robust against the oscillator temperature. Moreover, we have shown that this entanglement dynamics is strongly related to the stability of the normal modes. Taking mechanical damping effects into account, an analytical expression corresponding to the critical mechanical coupling strength, where the transition from stationary to dynamical entanglement occurs, is also reported. The proposed scheme is analyzed with experimentally realistic parameters, making it a promising means to realize macroscopic quantum entanglement within current state-of-the-art experimental setups.

arXiv:1712.09572Physical Review AFeb 26, 201859 citations

Quantum Phase Transition and Critical Phenomena

Amit Dutta, Chakrabarti, B K

Jan 1, 19980 citations

Disorder lines, modulation, and partition function zeros in free fermion models

P. N. Timonin, Gennady Y. Chitov

The modulation is analyzed from the analytical properties of zeros of the free fermionic partition function on the complex plane of wave numbers. It is shown how these properties are related to the oscillations of correlation functions. This approach can be used for analysis of phase transitions with local or nonlocal order parameters, as well as for the disorder lines. We find an infinite cascade of disorder lines at finite temperature in the quantum $XY$ chain (equivalent to free fermions). The well-known ground-state factorization on the disorder line, and consequently disentanglement, is shown to follow directly from analytical properties of this model on the complex plane. From the quantum-classical correspondence the results for the chain are used to detect the disorder lines in several frustrated two-dimensional Ising models. The present formalism can be applied to other fermionic models in two and three spatial dimensions. In particular, we find the temperature-dependent Fermi wave vector of oscillations in the degenerate gas of three-dimensional fermions, which naturally leads in the limit $T\ensuremath{\rightarrow}0$ to the definition of the Fermi energy as the surface of quantum criticality. The modulation is a very common phenomenon, and it occurs in a large variety of models. The important point is that all these modulation transitions can be related to the complex zeros of partition functions, as done in the present study.The modulation is analyzed from the analytical properties of zeros of the free fermionic partition function on the complex plane of wave numbers. It is shown how these properties are related to the oscillations of correlation functions. This approach can be used for analysis of phase transitions with local or nonlocal order parameters, as well as for the disorder lines. We find an infinite cascade of disorder lines at finite temperature in the quantum $XY$ chain (equivalent to free fermions). The well-known ground-state factorization on the disorder line, and consequently disentanglement, is shown to follow directly from analytical properties of this model on the complex plane. From the quantum-classical correspondence the results for the chain are used to detect the disorder lines in several frustrated two-dimensional Ising models. The present formalism can be applied to other fermionic models in two and three spatial dimensions. In particular, we find the temperature-dependent Fermi wave vector of oscillations in the degenerate gas of three-dimensional fermions, which naturally leads in the limit $T\ensuremath{\rightarrow}0$ to the definition of the Fermi energy as the surface of quantum criticality. The modulation is a very common phenomenon, and it occurs in a large variety of models. The important point is that all these modulation transitions can be related to the complex zeros of partition functions, as done in the present study.

arXiv:2105.01307Physical review. B./Physical review. BJul 6, 202111 citations

Micron-size superconducting quantum interference devices (

\mu

-SQUIDs) are highly-sensitive magnetic flux sensors where the critical current or the voltage is modulated by the magnetic flux. The so-called voltage read-out mode is nevertheless often hindered by thermal hysteresis.

\mu

-SQUIDs with improved thermal evacuation and small critical current can feature a phase-dynamic regime over a narrow bias-current and temperature range. Guided by a dynamic thermal model, we could widen these current and temperature ranges by using a shunt resistor. A significant increase in these ranges and, more strikingly, in the voltage oscillations magnitude is observed when the shunt is made of an adequate inductance in series with the resistor. An increase in inductance above a threshold value leads to relaxation oscillations in voltage. The large voltage modulation thus obtained offers an improved flux resolution in the voltage read-out mode down to 1.3 K.

XY

chain (equivalent to free fermions). The well-known ground-state factorization on the disorder line, and consequently disentanglement, is shown to follow directly from analytical properties of this model on the complex plane. From the quantum-classical correspondence the results for the chain are used to detect the disorder lines in several frustrated two-dimensional Ising models. The present formalism can be applied to other fermionic models in two and three spatial dimensions. In particular, we find the temperature-dependent Fermi wave vector of oscillations in the degenerate gas of three-dimensional fermions, which naturally leads in the limit $T\ensuremath{\rightarrow}0$ to the definition of the Fermi energy as the surface of quantum criticality. The modulation is a very common phenomenon, and it occurs in a large variety of models. The important point is that all these modulation transitions can be related to the complex zeros of partition functions, as done in the present study.