London’s National Physical Laboratory (NPL) Extends Quantum Tomography with Swabian Instruments’ Time Taggers

| 日期 10 February 2025

Figure 1. The schematic represents the experimental setup, where the system is fully fiber-coupled, and beamsplitters and mirrors are symbolic. The elements enclosed by the dashed red line represent the qPNRD. The histogram curve (red bars) provides an example of the power distribution recorded by the power meter for a given attenuation setting in the VOA. Figure adapted from [1].

Scientific background of quantum tomography of a quasi-photon-number-resolving detector (qPNRD)

Photon number resolution (PNR) is an advanced detection technique used to assign the exact number of photons involved in a detection event, providing precise photon-number measurements. This capability is pivotal in areas like quantum mechanics research, quantum metrology, and quantum optical technologies. Recent advancements in the field involve PNR-resolving SNSPDs and state-of-the-art timing electronics to resolve photon numbers with simplified experimental setups.

In contrast, quasi-photon-number-resolving (qPNR) approaches employ multiple single-photon detectors that measure a demultiplexed optical signal to probabilistically approximate photon numbers. While it lacks the precision of true PNR detectors, setups involving qPNR detectors (qPNRD) offer several advantages, including lower cost, and reduced complexity, making it a practical choice for many real-world applications.

Traditionally, the characterization of qPNRDs has relied on quantum tomography based on the positive operator-valued measure (POVM) framework. Building on this, researchers at the National Physical Laboratory (NPL) in London, UK, have successfully integrated Bayesian formalism into the POVM framework, enabling enhanced characterization and broader applicability of qPNRDs in quantum tomography, as shown in the latest publication [1].

To successfully characterize qPNRDs, timing electronics with high speed and low jitter are necessary. Swabian Instruments’ TIme Taggers are well suited to address these requirements.

Elevating quantum tomography with Time Tagger Ultra

To achieve groundbreaking results in quantum tomography, researchers at NPL employed a meticulously designed experimental setup. The foundation of this experiment relies on precise, high-speed, and low-jitter photon detection—capabilities delivered by Time Tagger Ultra .

A gain-switched laser was used to emit a finely controlled optical signal. A variable optical attenuator (VOA) adjusts the signal’s optical power, which is then split using a 50:50 beamsplitter. From there:

• Output One: Directed to a high-sensitivity optical power meter for optical power measurements.
• Output Two: Routed to a balanced splitter with four outputs, each connected to a superconducting nanowire single-photon detector (SNSPD). The SNSPDs are known for their exceptional sensitivity and precision in detecting photons. Detection events are recorded with Time Tagger Ultra, which delivers: 1 ps digital resolution, 8 ps RMS jitter, and 2.1 ns deadtime .

The Time Tagger Ultra stands out for this application for several reasons:

• Speed and Accuracy: Its high-speed capabilities align seamlessly with the optical signal’s repetition rate, while its low jitter ensures precise detection event timestamps.
• Efficiency in Data Analysis: “ The replay method within the TimeTagger.py module is a significant time-saver during data analysis. It has saved me numerous lines of code and exhibits excellent performance,” - the leading scientist at NPL, Dr. Ted S. Santana, said.

By leveraging the Time Tagger Ultra, researchers at NPL have significantly advanced its quantum tomography experiments. According to Dr. Ted S. Santana: “Time Tagger Ultra is a truly plug-and-play device with intuitive and user-friendly software. Its specifications meet the requirements of most of our experiments”.

Through the integration of Swabian Instruments’ Time Tagger technology, NPL finds solutions for more accurate and efficient quantum tomography, ensuring its place at the forefront of quantum measurement innovations.

Dr. Ted S. Santana’s Testimonial

• “The replay method within the TimeTagger.py module is a significant time-saver during data analysis. It has saved me numerous lines of code and exhibits excellent performance.”

• “My experience with the Swabian Time Tagger has been excellent. It is a truly plug-and-play device with intuitive and user-friendly software. Its specifications meet the requirements of most of our experiments.”

References

[1] Ted S. Santana, Christian Daniel Muñoz, Robert A. Starkwood, and Christopher J. Chunnilall, "Extending the quantum tomography of a quasi-photon-number-resolving detector," Opt. Express 32, 20350-20359 (2024)

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