Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2509.05621 · Journal of Physics A Mathematical and Theoretical

Modified quantum Wheatstone bridge based on current circulation

Vipul Upadhyay, Rahul Marathe

Published Mar 23, 2026• 0 citations
arXivHTMLPDF

Abstract

Abstract We investigate a simple fermionic system designed to detect an unknown hopping rate between two sites by analyzing current circulation. The system exploits geometric asymmetry and utilizes the connection between the additional energy degeneracy point (AEDP) and current circulation for precise parameter detection. In the low-temperature, low-bias regime, with baths’ chemical potentials aligned near the degenerate energy, a balanced Wheatstone bridge condition emerges when the direction of current circulation reverses, providing a direct means to determine the unknown hopping strength. We further examine the impact of environmental interactions, demonstrating that the device remains functional under moderately strong dephasing and particle losses, though extreme environmental effects eventually degrade performance. Extending the analysis to general operating conditions, it is seen that the device continues to function effectively at higher voltages and temperatures. Finally, an analysis of the quantum Fisher information qualitatively supports our findings, revealing a sharp increase in the coherence contribution and a corresponding decrease in the population contribution near the AEDP. These results highlight geometric asymmetry as a robust and practical tool for quantum metrology.

DOI
10.1088/1751-8121/ae55e2

Related papers

Current circulation near additional energy degeneracy points in quadratic Fermionic networks

Vipul Upadhyay, Rahul Marathe

Abstract We study heat and particle current circulation (CC) in quadratic Fermionic systems analysed using a general dissipative Lindbladian master equation. It was observed in an earlier study (Upadhyay et al 2023 Phys. Rev. E 107 034120) that CC occurs near the additional energy degeneracy point (AEDP) in Fermionic systems which have some form of asymmetry. We find general analytical expression to support this observation for quadratic Fermionic networks. We then apply these ideas to the Su–Schrieffer–Heeger (SSH) model with periodic boundary conditions and a tight binding model with unequal hopping strengths in the upper and lower branches. In both these cases, we find the specific conditions required for observing CC and study the behavior of these currents with various system parameters. We find that having unequal number of Fermionic sites in the upper and lower branches is enough for generating CC in the SSH model. However, this asymmetry is not adequate for the tight-binding model and we require unequal hopping strengths in the upper and lower branches to induce CC in this model. We also compare our results with the exact results obtained via the Non-equilibrium Green function formalism, and observe that the relationship between AEDP and CC also holds for the exact results. Finally, we observe that for certain system parameters, the onset point of particle and heat CC are not the same. Based on all these observations, we describe how carefully examining the energy spectrum of the system gives a great deal of information about the possibility and behavior of CC in Fermionic systems with asymmetries.

arXiv:2401.05140•Journal of Statistical Mechanics Theory and Experiment•Nov 25, 2024•2 citations

Detecting zero-point fluctuations with stochastic Brownian oscillators

A. López, Felipe Herrera

High-quality quantum oscillators are preferred for precision sensing of external physical parameters because if the noise level due to interactions with the environment is too high, metrological information can be lost due to quantum decoherence. On the other hand, stronger interactions with a thermal environment could be seen as a resource for new types of metrological schemes. We present a general amplification strategy that enables the detection of zero-point fluctuations using low-quality quantum oscillators at finite temperature. We show that by injecting a controllable level of multiplicative frequency noise in a Brownian oscillator, quantum deviations from the virial theorem can be amplified by a parameter proportional to the strength of the frequency noise at constant temperature. As an application, we suggest a scheme in which the virial ratio is used as a witness of the quantum fluctuations of an unknown thermal bath, either by measuring the oscillator energy or the heat current flowing into an ancilla bath. Our work expands the metrological capacity of low-quality oscillators and can enable new measurements of the quantum properties of thermal environments by sensing their zero-point contributions to system variables.

arXiv:2506.13952•Physical review. E•Nov 6, 2025•0 citations

Quantum metrology of a structured reservoir

Youssef Aiache, Asghar Ullah, Özgür Esat Müstecaplıoğlu +1 more

Accurately characterizing the properties of structured reservoirs is a key challenge in quantum systems and is of great importance for advances in quantum metrology and sensing. In this work, we employ a two-level system (qubit) as a probe, which is coupled to a structured reservoir consisting of an ancilla qubit and a Markovian environment modeled as a thermal bath. By exploiting non-Markovian dynamics, we systematically investigate the effectiveness of different interaction types between the probe and ancilla for estimating critical parameters, including temperature, ancilla frequency, and system-bath coupling strength. We quantify the precision of parameter estimation using quantum Fisher information (QFI) and analyze the system dynamics in both transient and steady-state regimes. Our findings demonstrate that non-Markovianity substantially enhances parameter estimation in the transient regime, with specific interactions facilitating sustained information backflow and yielding higher QFI values. However, the performance of these interactions is contingent on the parameter under estimation and the operational regime. For instance, certain interactions become prominent in the transient regime but exhibit diminished utility in the steady state, whereas others maintain their effectiveness even at equilibrium. These results stress the importance of judiciously selecting interactions adapted to specific estimation objectives and operational regimes.

arXiv:2503.16261•Physical Review A•May 28, 2025•5 citations

Quantum Sensing with Nanoelectronics: Fisher Information for an Applied Perturbation

George Mihailescu, Anthony Kiely, Andrew K. Mitchell

Quantum systems used for metrology can offer enhanced precision over their classical counterparts. The design of quantum sensors can be optimized by maximizing the quantum Fisher information (QFI), which characterizes the precision of parameter estimation for an ideal measurement. Here we consider the response of a quantum system as a means to estimate the strength of a weak external perturbation. General expressions for the QFI in the nonequilibrium steady-state are derived, which hold for arbitrary interacting many-body systems at finite or zero temperature, and can be related to susceptibilities or linear-response transport coefficients. For quantum dot nanoelectronics devices, we show that electron interactions can lead to *exponential* scaling of the QFI with system size, highlighting that quantum resources can be utilized in the full Fock space. The precision estimation of voltages and fields can also be achieved by practical measurements. In particular, we show that current-based metrology in quantum circuits can leverage many-body effects for enhanced sensing.

arXiv:2406.18662•Jun 26, 2024•1 citation

A proposal for direct measurement on the quantum geometric potential

Jianda Wu

The quantum geometric potential is a gauge invariant carrying novel geometric features between any two energy levels or bands in quantum systems. In generic time-dependent systems it gives a vital physical modification for the instantaneous energy gaps, laying down more appropriate quantum adiabatic conditions for both non-degenerate and degenerate systems. Remarkably, for generic parameterized quantum systems, the integration of the quantum geometric potential on a closed loop leads to a novel type of quantized winding number, which is a quantum counterpart of the Gauss-Bonnet theorem. The effects of the quantum geometric potential had been indirectly supported by the experiments on the quantum adiabatic evolution, however, a direct experimental observation so far is lacking. In this paper we propose an interference measurement to directly probe the quantum geometric potential, where the relevant parameters are easily accessible by current experimental apparatus. A direct confirmation of this new physical quantity could motive further theoretical and experimental investigations as well as its potential real applications.

arXiv:1801.00190•Dec 30, 2017•0 citations

Multi-Parameter Multi-Critical Metrology of the Dicke Model

Luca Previdi, Yilun Xu, Qiongyi He +1 more

Critical quantum metrology exploits the hypersensitivity of quantum systems near phase transitions to achieve enhanced precision in parameter estimation. While single-parameter estimation near critical points is well established, the simultaneous estimation of multiple parameters, which is essential for practical sensing applications, remains challenging. This difficulty arises from sloppiness, a phenomenon that typically renders the quantum Fisher information matrix (QFIM) singular or nearly singular. In this work, we demonstrate that multiparameter critical metrology is not only feasible but can also retain divergent precision scaling, provided one accepts a trade-off in the scaling exponent. Using the ground state of the single-cavity Dicke model (DM), we show that two Hamiltonian parameters can be simultaneously estimated with a scalar variance bound scaling as the square root of the critical parameter. This overcomes the inherent sloppiness by leveraging higher-order contributions to the QFIM. To recover the optimal quadratic scaling, we introduce the Dicke dimer (DD) with photon hopping. In this extended model, a triple point in the phase diagram enables the simultaneous closure of two excitation gaps, which effectively increases the rank of the QFIM and restores the ideal single-parameter scaling for specific parameter pairs. Furthermore, we extend our analysis to dissipative settings subject to photon loss. Finally, we establish a connection between the derived critical scalings and the fundamental state preparation time, providing a unified framework to operationally compare different sensing strategies. Our results demonstrate that critical quantum metrology can be made robust against dissipation and scalable to multiparameter scenarios, paving the way for practical quantum sensors operating near phase transitions.

quant-pharXiv:2603.03451•Mar 5, 2026•0 citations
Abstract We investigate a simple fermionic system designed to detect an unknown hopping rate between two sites by analyzing current circulation. The system exploits geometric asymmetry and utilizes the connection between the additional energy degeneracy point (AEDP) and current circulation for precise parameter detection. In the low-temperature, low-bias regime, with baths’ chemical potentials aligned near the degenerate energy, a balanced Wheatstone bridge condition emerges when the direction of current circulation reverses, providing a direct means to determine the unknown hopping strength. We further examine the impact of environmental interactions, demonstrating that the device remains functional under moderately strong dephasing and particle losses, though extreme environmental effects eventually degrade performance. Extending the analysis to general operating conditions, it is seen that the device continues to function effectively at higher voltages and temperatures. Finally, an analysis of the quantum Fisher information qualitatively supports our findings, revealing a sharp increase in the coherence contribution and a corresponding decrease in the population contribution near the AEDP. These results highlight geometric asymmetry as a robust and practical tool for quantum metrology.
Abstract We study heat and particle current circulation (CC) in quadratic Fermionic systems analysed using a general dissipative Lindbladian master equation. It was observed in an earlier study (Upadhyay et al 2023 Phys. Rev. E 107 034120) that CC occurs near the additional energy degeneracy point (AEDP) in Fermionic systems which have some form of asymmetry. We find general analytical expression to support this observation for quadratic Fermionic networks. We then apply these ideas to the Su–Schrieffer–Heeger (SSH) model with periodic boundary conditions and a tight binding model with unequal hopping strengths in the upper and lower branches. In both these cases, we find the specific conditions required for observing CC and study the behavior of these currents with various system parameters. We find that having unequal number of Fermionic sites in the upper and lower branches is enough for generating CC in the SSH model. However, this asymmetry is not adequate for the tight-binding model and we require unequal hopping strengths in the upper and lower branches to induce CC in this model. We also compare our results with the exact results obtained via the Non-equilibrium Green function formalism, and observe that the relationship between AEDP and CC also holds for the exact results. Finally, we observe that for certain system parameters, the onset point of particle and heat CC are not the same. Based on all these observations, we describe how carefully examining the energy spectrum of the system gives a great deal of information about the possibility and behavior of CC in Fermionic systems with asymmetries.
High-quality quantum oscillators are preferred for precision sensing of external physical parameters because if the noise level due to interactions with the environment is too high, metrological information can be lost due to quantum decoherence. On the other hand, stronger interactions with a thermal environment could be seen as a resource for new types of metrological schemes. We present a general amplification strategy that enables the detection of zero-point fluctuations using low-quality quantum oscillators at finite temperature. We show that by injecting a controllable level of multiplicative frequency noise in a Brownian oscillator, quantum deviations from the virial theorem can be amplified by a parameter proportional to the strength of the frequency noise at constant temperature. As an application, we suggest a scheme in which the virial ratio is used as a witness of the quantum fluctuations of an unknown thermal bath, either by measuring the oscillator energy or the heat current flowing into an ancilla bath. Our work expands the metrological capacity of low-quality oscillators and can enable new measurements of the quantum properties of thermal environments by sensing their zero-point contributions to system variables.
Accurately characterizing the properties of structured reservoirs is a key challenge in quantum systems and is of great importance for advances in quantum metrology and sensing. In this work, we employ a two-level system (qubit) as a probe, which is coupled to a structured reservoir consisting of an ancilla qubit and a Markovian environment modeled as a thermal bath. By exploiting non-Markovian dynamics, we systematically investigate the effectiveness of different interaction types between the probe and ancilla for estimating critical parameters, including temperature, ancilla frequency, and system-bath coupling strength. We quantify the precision of parameter estimation using quantum Fisher information (QFI) and analyze the system dynamics in both transient and steady-state regimes. Our findings demonstrate that non-Markovianity substantially enhances parameter estimation in the transient regime, with specific interactions facilitating sustained information backflow and yielding higher QFI values. However, the performance of these interactions is contingent on the parameter under estimation and the operational regime. For instance, certain interactions become prominent in the transient regime but exhibit diminished utility in the steady state, whereas others maintain their effectiveness even at equilibrium. These results stress the importance of judiciously selecting interactions adapted to specific estimation objectives and operational regimes.
Quantum systems used for metrology can offer enhanced precision over their classical counterparts. The design of quantum sensors can be optimized by maximizing the quantum Fisher information (QFI), which characterizes the precision of parameter estimation for an ideal measurement. Here we consider the response of a quantum system as a means to estimate the strength of a weak external perturbation. General expressions for the QFI in the nonequilibrium steady-state are derived, which hold for arbitrary interacting many-body systems at finite or zero temperature, and can be related to susceptibilities or linear-response transport coefficients. For quantum dot nanoelectronics devices, we show that electron interactions can lead to *exponential* scaling of the QFI with system size, highlighting that quantum resources can be utilized in the full Fock space. The precision estimation of voltages and fields can also be achieved by practical measurements. In particular, we show that current-based metrology in quantum circuits can leverage many-body effects for enhanced sensing.
The quantum geometric potential is a gauge invariant carrying novel geometric features between any two energy levels or bands in quantum systems. In generic time-dependent systems it gives a vital physical modification for the instantaneous energy gaps, laying down more appropriate quantum adiabatic conditions for both non-degenerate and degenerate systems. Remarkably, for generic parameterized quantum systems, the integration of the quantum geometric potential on a closed loop leads to a novel type of quantized winding number, which is a quantum counterpart of the Gauss-Bonnet theorem. The effects of the quantum geometric potential had been indirectly supported by the experiments on the quantum adiabatic evolution, however, a direct experimental observation so far is lacking. In this paper we propose an interference measurement to directly probe the quantum geometric potential, where the relevant parameters are easily accessible by current experimental apparatus. A direct confirmation of this new physical quantity could motive further theoretical and experimental investigations as well as its potential real applications.
Critical quantum metrology exploits the hypersensitivity of quantum systems near phase transitions to achieve enhanced precision in parameter estimation. While single-parameter estimation near critical points is well established, the simultaneous estimation of multiple parameters, which is essential for practical sensing applications, remains challenging. This difficulty arises from sloppiness, a phenomenon that typically renders the quantum Fisher information matrix (QFIM) singular or nearly singular. In this work, we demonstrate that multiparameter critical metrology is not only feasible but can also retain divergent precision scaling, provided one accepts a trade-off in the scaling exponent. Using the ground state of the single-cavity Dicke model (DM), we show that two Hamiltonian parameters can be simultaneously estimated with a scalar variance bound scaling as the square root of the critical parameter. This overcomes the inherent sloppiness by leveraging higher-order contributions to the QFIM. To recover the optimal quadratic scaling, we introduce the Dicke dimer (DD) with photon hopping. In this extended model, a triple point in the phase diagram enables the simultaneous closure of two excitation gaps, which effectively increases the rank of the QFIM and restores the ideal single-parameter scaling for specific parameter pairs. Furthermore, we extend our analysis to dissipative settings subject to photon loss. Finally, we establish a connection between the derived critical scalings and the fundamental state preparation time, providing a unified framework to operationally compare different sensing strategies. Our results demonstrate that critical quantum metrology can be made robust against dissipation and scalable to multiparameter scenarios, paving the way for practical quantum sensors operating near phase transitions.