Quantum Enhancement in Precision Using 100-Photon Fock States

In the realm of quantum information science, the pursuit of precision has become a grand expedition, ceaselessly pushing the boundaries of what is measurable to the limits set by the fundamental laws of physics. In a recent groundbreaking study published in Nature Physics, Deng et al. have demonstrated a significant stride in this journey by achieving Heisenberg-limited quantum metrology using large Fock states with up to 100 photons in a superconducting microwave cavity. 
The Pursuit of Precision: Beyond Classical Limits
The precision of classical measurements is often limited by the standard quantum limit (SQL), a boundary set by the inherent quantum fluctuations of the systems being measured. However, the Heisenberg limit (HL) offers a tantalizing promise of surpassing these limits, suggesting a precision improvement by a factor of 1/√N, where N is the number of particles or excitations involved in the measurement process.
Harnessing Quantum Fock States
The researchers’ approach to breaching the SQL involved the use of large photon-number Fock states within a high-quality superconducting microwave cavity. Fock states are unique in that they possess a definite number of particles, in this case, photons, which allows for exquisite control and manipulation in quantum systems.
The team led by Yuan Xu at the Shenzhen International Quantum Academy has developed a programmable photon number filter that efficiently generates Fock states with up to 100 photons, which is the largest microwave Fock state ever realized. This was no small feat, as the generation of such states typically requires complex procedures and a high level of precision.
Precision Measurement: Displacement and Phase
Using these Fock states, the researchers conducted displacement and phase measurements that demonstrated a precision scaling close to the Heisenberg limit. They achieved a maximum metrological gain of up to 14.8 dB, a significant leap from conventional measurement techniques.
In the displacement sensing experiment, a small displacement shift in the quantum state was induced, and the researchers were able to measure this shift with a remarkable accuracy. The use of Fock states allowed them to surpass the SQL, achieving a precision enhancement that scales with the square root of the number of photons, as predicted by the Heisenberg limit.
Similarly, in phase sensing, the researchers applied a phase rotation to the Fock states and were able to determine the phase shift with a high precision. This experiment also demonstrated a precision enhancement that scales with the square root of the average photon number, aligning with the Heisenberg limit.
Outlook and Conclusion
The practical applications of this research are vast and varied. With high-precision quantum metrology now within reach, we can envision transformative impacts across the radiometry, the detection of weak forces, and the search for new particles, such as dark matter axions.
The demonstrated achievement of Heisenberg-limited quantum metrology using 100-photon Fock states represents a significant milestone in the ongoing quantum journey. It is a testament to the power of quantum mechanics to transcend classical limitations, heralding a new stage of the potential revolutions in precision measurement technology. This research guides us toward a future where the quantum world is not just a subject of theoretical fascination but a driving force for technological advancement.
Link: https://www.nature.com/articles/s41567-024-02619-5