A versatile approach to realize quantum-enhanced metrology with large Fock states

The collecting of highly precise measurements can enable research developments and technological advancements in numerous fields. In physics, high-precision measurements can unveil new phenomena and experimentally validate theories.

Quantum-enhanced metrology techniques are emerging methods that enable the collection of precise measurements utilizing non-classical states. While these techniques could theoretically outperform classical approaches, reliably manipulating non-classical states to achieve high-precision measurements has so far proved challenging.

Researchers at the International Quantum Academy, Southern University of Science and Technology, and University of Science and Technology of China recently introduced a new approach to realize quantum-enhanced metrology. Their proposed approach, introduced in Nature Physics, was found to enable the efficient generation of large Fock states with up to almost 100 photons.

“Our recent research primarily focused on the high-precision measurement of weak microwave electromagnetic fields,” Yuan Xu, co-author of the paper, told Phys.org. “We found that microwave Fock states in a superconducting cavity are promising candidates, as they exhibit ultrafine interference structural features in phase space.

“A small shift or displacement of these states induced by a weak microwave field can be detected with high precision due to the ultrafine interference patterns of Fock states. The larger the photon number of the Fock state, the finer the interference fringes presented, and thus the more precise the detection could be.”

To realize a significant metrological gain above classical metrology techniques using quantum-mechanical principles, Xu and his colleagues set out to devise an approach that would enable the generation of Fock states with up to 100 photons. Their proposed method relies on the use of two distinct types of photon number filters.

“We employed two types of photon number filters (PNF)—sinusoidal PNF and Gaussian PNF—to generate large Fock states by utilizing the photon-number-dependent response of an ancilla qubit coupled to the cavity,” explained Xu. “These PNFs can selectively filter out specific photon numbers based on the state of the ancilla qubit.”

To implement the sinusoidal PNF, the researchers inserted a conditional rotation into a Ramsey-type sequence and projected the ancilla qubit in the ground state. This operation acts as a grating that periodically blocks specific photon numbers of the cavity states.

In contrast, the second photon number filter they used, called Gaussian PNF, applies a qubit flip pulse with a Gaussian envelope. This compresses the distribution of photon numbers, concentrating on a subspace that is centered around a desired Fock state.

“The combination of these two PNFs facilitates the efficient generation of large Fock states,” said Xu. “A key advantage of this method is its efficiency, as it allows for the generation of large Fock states with a circuit depth that scales logarithmically with the photon number, making it more efficient than previous proposals that required polynomial scaling.

“Furthermore, this method is hardware-efficient and more practical for generating Fock states with a large number of photons, which is crucial for achieving quantum-enhanced metrology with high precision.”

The team’s approach has so far proved to offer a viable route to implement hardware-efficient quantum metrology using large Fock states in a single bosonic mode. Notably, the approach is also highly versatile and could thus be easily extended to other physical platforms, such as mechanical and optical systems.

“We introduced a new quantum control method for generating Fock states with a substantial number of photons; and set a new record of Fock state generation and metrological gain,” said Xu. “We successfully generated large Fock states containing up to 100 photons, which represents an order of magnitude increase over previous demonstrations and is the largest microwave Fock states to our knowledge.”

In initial tests, the approach for realizing quantum-enhanced metrology devised by Xu and his colleagues was found to significantly outperform classical metrology, enabling a metrological gain of 14.8 dB and thus approaching the Heisenberg limit.

Their work could soon enable the collection of more precise measurements, potentially leading to new exciting discoveries and observations rooted in various fields.

“First, our study benefits fundamental research by providing a testbed for theoretical predictions of highly non-trivial quantum effects in quantum optics and quantum mechanics,” said Xu. “Second, our hardware-efficient single-mode quantum metrology demonstrates remarkable potential for practical applications, including high-precision radiometry, weak force detection, and dark matter searches.”

The researchers hope that their recent research efforts will contribute to the collection of increasingly precise measurements, paving the way for advancements in various fields. In their next studies, they plan to continue advancing their method, focusing on two key research directions.

“First, we now aim to further improve the coherence performance of the quantum system and develop high-precision, scalable quantum control techniques to deterministically generate Fock states with higher photon numbers, thereby achieving a larger metrological gain,” said Xu.

“Second, we will explore the significant applications of the hardware-efficient quantum metrology scheme demonstrated here, particularly in areas such as the detection of weak electromagnetic fields and the search for dark matter.”

© 2024 Science X Network