Periodic Reporting for period 2 - STORMYTUNE (Spectral-Temporal Metrology with Tailored Quantum Measurements)
Reporting period: 2022-04-01 to 2024-08-31
Metrology explores the most efficient and precise way to perform measurements. This established area of study has considerable impact on our everyday lives. A GPS would not work without the capability to measure distances precisely, and spectral fingerprinting is an established technique to identify, e.g. drugs and hazardous materials. In recent years, researchers have begun to study metrology in the counterintuitive realm of quantum mechanics, so called quantum metrology. Surprisingly – or maybe not so, depending on whom you ask – it turns out that quantum properties such as entanglement can be highly beneficial for metrological tasks. Experiments have yielded measurement precision that goes beyond that of any classical measurement and to date, ever more demonstrations are reaching the ultimate precision limits set by quantum mechanics. These findings have two potential impacts: on the one hand, we can imagine measurements that simply cannot be implemented with classical means and that consequently enable hitherto unknown applications; on the other hand, we find that a better measurement can reach the same precision as a worse measurement in less time, leading to faster data acquisition. Interestingly, quantum metrology mainly focusses on measuring phases, with only few works considering spatial imaging. There is no comprehensive approach to measuring time or frequency using quantum mechanical methods, although many applications could benefit from such techniques.
This is where the work of STORMYTUNE comes in. We will develop a theoretical and experimental toolbox for time-frequency quantum metrology and explore possible avenues for improving applications using our methods. In contrast to other approaches to quantum metrology that mainly focus on using fragile probe states, we will investigate the achievable benefits when using quantum measurements and simple, robust probe states. Further, we aim to improve the performance of our techniques by adding the ideas of superresolution measurements and compressed sensing to time-frequency quantum metrology, thus reducing measurement times even further.
The STORMYTUNE consortium comprises world-leading scientists and industry partners, who are ideally positioned to achieve the project goals. For this research, we have identified three strategic objectives that will guide our efforts.
- Objective 1: Develop a time-frequency quantum metrology toolbox that comprises of the tools and methods for investigating the limits of temporal and spectral measurements using quantum mechanics.
- Objective 2: Investigate the limits of time-frequency quantum metrology with regards to the ultimate measurement precision, the resource consumption, and the ease of implementation.
- Objective 3: Implement proof-of-concept demonstrations that show a clear benefit of quantum metrology when compared to standard measurements and that exploit techniques from superresolution measurements and compressed sensing.
This is where the work of STORMYTUNE comes in. We will develop a theoretical and experimental toolbox for time-frequency quantum metrology and explore possible avenues for improving applications using our methods. In contrast to other approaches to quantum metrology that mainly focus on using fragile probe states, we will investigate the achievable benefits when using quantum measurements and simple, robust probe states. Further, we aim to improve the performance of our techniques by adding the ideas of superresolution measurements and compressed sensing to time-frequency quantum metrology, thus reducing measurement times even further.
The STORMYTUNE consortium comprises world-leading scientists and industry partners, who are ideally positioned to achieve the project goals. For this research, we have identified three strategic objectives that will guide our efforts.
- Objective 1: Develop a time-frequency quantum metrology toolbox that comprises of the tools and methods for investigating the limits of temporal and spectral measurements using quantum mechanics.
- Objective 2: Investigate the limits of time-frequency quantum metrology with regards to the ultimate measurement precision, the resource consumption, and the ease of implementation.
- Objective 3: Implement proof-of-concept demonstrations that show a clear benefit of quantum metrology when compared to standard measurements and that exploit techniques from superresolution measurements and compressed sensing.
We have built quantum detectors that are used in our laboratories to measure temporal and spectral properties with precisions at the ultimate quantum limit. This means that there are no better detectors, nor will there be better detectors. Our devices are doing the best job allowed by quantum mechanics. Why can we say that? Because we have also developed the underlying theoretical description. We can use the language of quantum information science to formulate the problems we are looking into. From this we derive the ultimate precision limit, which we then compare to our measurement results. STORMYTUNE partners have built experiments in four different countries. These are based on different hardware approaches and each is investigating different angles of time-frequency quantum metrology. In parallel, our theory framework helps us to understand the subtleties of time-frequency multi-parameter estimation and enables us to identify new application scenarios that can benefit from quantum measurements.
Some of the highlight results include:
- We have realized time-frequency superresolution measurements that outperform their classical analogues. We could demonstrate improved spectral and temporal resolution in different experimental systems, which highlights the general applicability of our results.
- We have combined compressed sensing techniques with quantum metrology. This enables the ressource efficient and rapid characterization of quantum states of light and fast measurements, where future measurement settings depend on current measurement outcomes.
- We have demonstrated time-frequency projections with a quantum memory. This approach combines the benefits of our toolbox with the potential applications of quantum memories in large-scale quantum networks.
- We have identified the precise benefits of using squeezing – a quantum effect whereby the fluctuations of the phase or amplitude of a light field are reduced – when characterizing frequency combs, established tools that are widely used for ultrafast spectroscopy and as ultra-precise clocks to date.
- We have built a time-frequency Shack-Hartmann-like detector that allows for the quantum limited measurement of the arrival time and carrier frequency of an unknown quantum signal and that facilitates a complete signal reconstruction without any a priori assumptions.
- Inspired by our research, we have implemented novel characterization techniques for ultrafast pulses, both classical and at the single-photon level, that require neither reconstruction algorithms nor known reference pulses. These techniques are enabled by the so-called multi-output quantum pulse gate, a device that facilitates the simultaneous projection of a signal onto different time-frequency modes.
- Going beyond the initial scope of the project, we demonstrated a scalable approach for the realisation of time-frequency linear optical networks that is based on a multi-channel squeezing source and time-frequency mode projections. The latter implement the linear optical network and can be rearranged according to the requirements of different applications. Combined with photon-counting measurements, this approach is suitable for quantum simulation and computing applications.
Some of the highlight results include:
- We have realized time-frequency superresolution measurements that outperform their classical analogues. We could demonstrate improved spectral and temporal resolution in different experimental systems, which highlights the general applicability of our results.
- We have combined compressed sensing techniques with quantum metrology. This enables the ressource efficient and rapid characterization of quantum states of light and fast measurements, where future measurement settings depend on current measurement outcomes.
- We have demonstrated time-frequency projections with a quantum memory. This approach combines the benefits of our toolbox with the potential applications of quantum memories in large-scale quantum networks.
- We have identified the precise benefits of using squeezing – a quantum effect whereby the fluctuations of the phase or amplitude of a light field are reduced – when characterizing frequency combs, established tools that are widely used for ultrafast spectroscopy and as ultra-precise clocks to date.
- We have built a time-frequency Shack-Hartmann-like detector that allows for the quantum limited measurement of the arrival time and carrier frequency of an unknown quantum signal and that facilitates a complete signal reconstruction without any a priori assumptions.
- Inspired by our research, we have implemented novel characterization techniques for ultrafast pulses, both classical and at the single-photon level, that require neither reconstruction algorithms nor known reference pulses. These techniques are enabled by the so-called multi-output quantum pulse gate, a device that facilitates the simultaneous projection of a signal onto different time-frequency modes.
- Going beyond the initial scope of the project, we demonstrated a scalable approach for the realisation of time-frequency linear optical networks that is based on a multi-channel squeezing source and time-frequency mode projections. The latter implement the linear optical network and can be rearranged according to the requirements of different applications. Combined with photon-counting measurements, this approach is suitable for quantum simulation and computing applications.
During the project, we have developed an extensive theory framework, which expands the limits of our understanding of quantum metrology. We have built novel devices that allow phase-sensitive time-frequency measurements that reach the ultimate precision, even in real-world experiments. We used these devices to demonstrate novel applications, both quantum and quantum-inspired. Using our extensive theory framework, we have improved on these applications and made them more ressource efficient, while at the same time removing the need for any a priori knowledge. Our methods of extracting the maximum information from incomplete data can be of interest to other scientific disciplines that are limited by low signal levels or require the highest possible precision. Examples include astronomy, gravitational wave sensing, and fundamental tests of general relativity. STORMYTUNE can potentially help to advance progress in these disciplines and thus advance science as such.