Quantum Exceptional Point Sensors: Enhancing Sensitivity, Precision in Quantum Sensing Field

Quantum exceptional point (EP) sensing, a new field of study, use exceptional points for high-precision sensing of physical parameters. The EP can significantly enhance the sensitivity of these sensors. Researchers have now established a connection between Quantum Fisher Information (QFI) and the order of the EP, which could be crucial for developing more sensitive quantum sensors. The study also suggests that the sensitivity of quantum EP sensors can increase exponentially with system size, opening up the possibility of designing novel quantum EP sensors through size-mode engineering. This could revolutionize quantum sensing, but further research is needed.

What is Quantum Exceptional Point Sensing?

Quantum exceptional point (EP) sensing is a relatively new field of study that has seen significant progress in recent years. The concept revolves around the use of exceptional points, which are degenerate points of non-Hermitian systems where two or more eigenstates coalesce. These points have emerged as a novel platform for achieving high precision sensing of physical parameters. In a classical system, the high sensitivity stems from the scaling of the eigenspectrum of a typical second-order EP, leading to a divergent spectrum response rate under a perturbation of a physical parameter deviated from the EP. For a higher order EP, the divergence can be more substantial to achieve higher sensitivity.

While EP-based sensing is well studied in classical open systems like gain-loss nanophotonics, its generalization to a quantum system poses a fundamental challenge. In an open quantum system, the intrinsic Langevin noises may break the underlying symmetry that protects the EP, rendering the conceptual difficulty for even defining EP-based quantum sensor. However, it was recently shown that an EP could emerge from the dynamical evolution matrix of the Hermitian quadratic bosonic Hamiltonian, thus avoiding Langevin noise. Around the EP, the quantum dynamics are very sensitive to the small perturbation of the parameter, therefore, can be utilized as a quantum EP sensor.

How is Quantum Fisher Information Related to Quantum EP Sensors?

In quantum sensing, quantum Fisher information (QFI) is one main characteristic quantity that provides a low bound for sensing precision through quantum Cramér-Rao bound. QFI is very different from the divergence of the spectrum response rate that characterizes classical EP-based sensors. It is unclear how the scaling of the quantum EP spectrum is connected with the behavior of the QFI and whether there exists certain universal scaling of the QFI at/around the EP.

To address these questions, researchers studied the QFI in a generic multimode bosonic quadratic Hamiltonian, which is Hermitian but its Heisenberg equation of motion is governed by a non-Hermitian dynamical matrix, yielding the EP physics. They derived an analytic formula of the QFI that is generally hard to calculate even numerically for multimode quadratic Hamiltonians due to the exponentially large Hilbert space of particle numbers.

What are the Findings of the Study on Quantum EP Sensors?

The study found a universal scaling of the QFI at an Mth order EP for a large time, which establishes the connection between the QFI and the order of the EP. From the analytic formula and scaling relation, it was shown that EP can significantly enhance the sensitivity. The achievable scaling showcases the QFI can grow much faster over time than non-EP sensors with typically scaling. Different from the divergence of the spectrum response rate, there is no divergence of the QFI at EP due to the continuity of the QFI formula, therefore, the large EP sensitivity enhancement can be achieved for parameters close to the EP.

In an N-mode bosonic Kitaev chain near the EP, the QFI per particle at a fixed time has an exponential scaling, which indicates the sensitivity of quantum EP sensor can increase exponentially with the system size, paving the way for designing novel quantum EP sensors through size-mode engineering.

What is the Significance of the Study on Quantum EP Sensors?

The study on quantum EP sensors is significant as it establishes the connection between two important fields: non-Hermitian EP dynamics and quantum sensing. The findings may find important applications in quantum information and quantum non-Hermitian physics. The study also provides a new perspective on the scaling of QFI and the order of the EP, which could be crucial for the development of more sensitive and efficient quantum sensors.

Moreover, the study also opens up the possibility of designing novel quantum EP sensors through size-mode engineering, which could potentially revolutionize the field of quantum sensing. The exponential scaling of the QFI per particle at a fixed time in an N-mode bosonic Kitaev chain near the EP indicates that the sensitivity of quantum EP sensor can increase exponentially with the system size. This could lead to the development of quantum sensors with unprecedented sensitivity and precision.

What are the Future Prospects of Quantum EP Sensors?

The future of quantum EP sensors looks promising. The study has shown that the sensitivity of quantum EP sensor can increase exponentially with the system size, which could lead to the development of quantum sensors with unprecedented sensitivity and precision. This could have wide-ranging applications in various fields, including quantum information and quantum non-Hermitian physics.

Moreover, the study also opens up the possibility of designing novel quantum EP sensors through size-mode engineering. This could potentially revolutionize the field of quantum sensing, leading to the development of more efficient and sensitive quantum sensors. However, more research is needed to fully understand the potential of quantum EP sensors and to overcome the challenges associated with their implementation.