Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2601.14565

Programming Quantum Measurements of Time inside a Complex Medium

Dylan Danese, Vatshal Srivastav, Will McCutcheon, Saroch Leedumrongwatthanakun, Mehul Malik

quant-phphysics.opticsSubmitted Jan 21, 2026• Announced Jan 22, 2026• 0 citations• Revised Mar 19, 2026 (v2)
v1 · Jan 21, 2026v2 · Mar 19, 2026
arXivHTMLPDF

Abstract

The temporal degree-of-freedom of light is incredibly powerful for modern quantum technologies, enabling large-scale quantum computing architectures and record key-rates in quantum key distribution. However, the generalized measurement of large and complex quantum superpositions of the time-of-arrival of a photon remains a unique experimental challenge. Conventional methods based on unbalanced Franson-type interferometers scale poorly with dimension, requiring multiple cascaded devices and active phase stabilization. In addition, these are limited by construction to a restricted set of phase-only superposition measurements. Here we show how the coupling of spatial and temporal information inside a single multi-mode fiber can be harnessed to program completely generalized measurements for high-dimensional superpositions of photonic time-bin. Using the multi-spectral transmission matrix of the fiber, we find special sets of spatial modes that experience distinct dispersive delays through the fiber. By exciting coherent superpositions of these spatial modes, we engineer the equivalent of large, unbalanced multi-mode interferometers inside the fiber and use them to perform high-quality measurements of arbitrary time-bin superpositions in up to dimension 11. The single fiber functions as a scalable, common-path interferometer for time-bin qudits that significantly eases the experimental overheads of standard approaches based on unbalanced Franson-type interferometers, serving as an essential tool for quantum technologies that harness the temporal properties of light.

Comments
8 + 10 pages, 5 + 4 figs

Related papers

Programming quantum measurements of time inside a multimode fibre

Mehul Malik, Dylan Danese, Vatshal Srivastav +2 more

The temporal degree-of-freedom of light is incredibly exciting for many quantum technologies, ranging from photonic quantum computing to quantum key distribution. The generalized measurement of large and complex superpositions of the time-of-arrival of a photon presents a unique experimental challenge. Here we show how the coupling of spatial and temporal information inside a multi-mode fiber (MMF) can be harnessed to program generalized measurements for large photonic time-bin qudits. By exciting superpositions of special sets of spatial modes that are temporally unscattered through the fiber, we engineer arbitrary measurements of photon time-bins in dimensions up to 11. The single fiber serves as a scalable, common-path interferometer for time-bin qudits that significantly eases the experimental overheads of standard approaches based on unbalanced Franson-type interferometers.

Complex Light and Optical Forces•Mar 5, 2026•0 citations

Programmable Generalized Time-Bin Measurements using Complex Media

Vatshal Srivastav, Dylan Danese, Saroch Leedumrongwatthanakun +2 more

We harness the spatio-temporal coupling of light inside a commercial step-index multi-mode fibre to program generalized projective measurements for photonic time-bin in dimension up to 7 and use them to certify high-dimensional time-bin entanglement.

Frontiers in Optics•Jan 1, 2024•1 citation

Programming 7-dimensional time-bin measurements inside a multi-mode fiber

Dylan Danese, Vatshal Srivastav, Saroch Leedumrongwatthanakun +2 more

We program generalized projective measurements for high-dimensional pho-tonic time-bins by harnessing spatial-mode dispersion inside a commercial multi-mode fiber. We characterize the measurements in the time-domain via quantum process tomography, certifying an average fidelity of 93.22±0.32%.

•Jan 1, 2025•0 citations

High-Dimensional Quantum Photonics: Roadmap

Mehul Malik, Micheal Kues, Takuya Ikuta +30 more

The field of high-dimensional quantum photonics involves the use of multimode photonic degrees-of-freedom such as the spatial, temporal, or spectral structure of light to encode multi-level quantum states. Recent years have seen rapid progress in the development of methods to generate, manipulate, and distribute such quantum states of light and their use in a range of quantum technology applications that offer practical advantages over conventional qubit-based approaches. High-dimensional quantum states of light encoded in photonic time-bins, frequency-bins, transverse-spatial modes, waveguide paths, and temporal modes have enabled noise-robust fundamental tests of quantum mechanics, error-resilient and high-capacity quantum communication protocols, andas well as efficient approaches for quantum information processing, to name just a few examples. However, research in this field has progressed fairly independently, with little exchange across different photonic degrees-of-freedom or between experiment and theory and no comprehensive comparison between degrees-of-freedom. This roadmap aims to bridge this gap by surveying progress in each area and identifying shared challenges and opportunities that cut across two or more photonic degrees-of-freedoms. We review early work and state-of-the-art experimental techniques under development for high-dimensional quantum states encoded in single and entangled photons, as well as theoretical tools for their measurement and certification. We outline the main outstanding challenges for theory and each experimental degree-of-freedom, identifying promising future directions of research that may enable these to be overcome. We end by discussing interconnections and shared challenges centered around their distribution, measurement, and manipulation, with a view towards their integration into next-generation quantum technology platforms and applications.

quant-pharXiv:2604.06528•Apr 9, 2026•1 citation

Removing Phase Ambiguity in Fiber-Based Interferometers for Coherent Time-Bin Operations

Piotr Roztocki, Mehedi Islam, Christian Reimer +6 more

Time is a practical and robust degree of freedom for the encoding of quantum information. Qubits encoded in so-called `time-bins', allowing a discrete superposition of two potential arrival times, have their entanglement preserved even over long propagation distances in standard fiber networks [1]. Time has also been used for the preparation of more complex quantum systems, such as hyper-entangled and cluster states [2]. These qualities put time-bin encoding at the center of applications ranging from quantum state preparation through to quantum communications and information processing. One of the hallmarks of the scheme is that a nonlinear element has to be pumped with phase-coherent double-pulses, which can be achieved by using unbalanced interferometers [1], making their phase stability the key determinant of both state generation and analysis accuracy. However, the phase ambiguity arising from the periodicity of feedback signals [3], as well as the difficulty of stabilizing on interference maxima/minima, leave progress to be made in fiberbased interferometry for time-bin encodings.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2019•0 citations

Ultrafast Metrology in the Quantum Domain

Jean-Philippe W. MacLean

Single photons are a natural platform for quantum technologies as they support entanglement in many degrees of freedom and are inherently well protected from a detrimental type of noise called decoherence. In order to fully exploit photons for quantum technologies, it will be necessary to be able to shape, control, and measure their properties in all degrees of freedom: space, time, frequency, and polarization. \n \n The time-frequency degree of freedom of light is of particular interest for quantum information tasks as it supports various encodings, including frequency bins and time bins, and is intrinsically robust for propagation through long-distance fibre links. Applications which harness quantum correlations in this degree of freedom, referred to as energy-time entanglement, include dispersion cancellation and high-dimensional quantum key distribution. However, detection of this entanglement and observation of these effects requires time resolution beyond the capabilities of current photon detectors. Thus, for operations on ultrafast time scales, more powerful and complex methods are required. \n \n In this thesis, we use a nonlinear technique known as optical gating to surpass the limitations in current detectors and measure single photon pairs, improving the time resolution by two orders of magnitude. When a single photon enters a nonlinear medium at the same time as a strong laser pulse, it may upconvert to a higher energy photon. The strong laser pulse effectively acts as an ultrafast shutter or gate and this creates a high resolution snapshot of the photon in time. Optical gating in conjunction with single photon spectrometers then allow us to measure both the spectral and temporal features of photons on subpicosecond time scales. \n \n These high resolution measurements enable us to explore a host of quantum effects which remained previously inaccessible. First, we directly observe energy-time entanglement, analogous to Einstein-Rosen-Podolsky correlations but \\emph{in frequency and time}. Then, with full control over the dispersion of each photon, we observe nonlocal dispersion cancellation on femtosecond time scales. We also explore ultrafast interferometry in the quantum domain by temporally resolving two-photon interference from a Franson interferometer and observe a violation of the CHSH-Bell inequality. Finally, we show that, using these measurements, it is possible to reconstruct a two-photon energy-time entangled state. Such measurement capabilities will be essential to precisely control both the spectral and temporal shape of entangled photons and to develop new applications in quantum state engineering.

•Feb 15, 2019•1 citation
The temporal degree-of-freedom of light is incredibly powerful for modern quantum technologies, enabling large-scale quantum computing architectures and record key-rates in quantum key distribution. However, the generalized measurement of large and complex quantum superpositions of the time-of-arrival of a photon remains a unique experimental challenge. Conventional methods based on unbalanced Franson-type interferometers scale poorly with dimension, requiring multiple cascaded devices and active phase stabilization. In addition, these are limited by construction to a restricted set of phase-only superposition measurements. Here we show how the coupling of spatial and temporal information inside a single multi-mode fiber can be harnessed to program completely generalized measurements for high-dimensional superpositions of photonic time-bin. Using the multi-spectral transmission matrix of the fiber, we find special sets of spatial modes that experience distinct dispersive delays through the fiber. By exciting coherent superpositions of these spatial modes, we engineer the equivalent of large, unbalanced multi-mode interferometers inside the fiber and use them to perform high-quality measurements of arbitrary time-bin superpositions in up to dimension 11. The single fiber functions as a scalable, common-path interferometer for time-bin qudits that significantly eases the experimental overheads of standard approaches based on unbalanced Franson-type interferometers, serving as an essential tool for quantum technologies that harness the temporal properties of light.
The temporal degree-of-freedom of light is incredibly exciting for many quantum technologies, ranging from photonic quantum computing to quantum key distribution. The generalized measurement of large and complex superpositions of the time-of-arrival of a photon presents a unique experimental challenge. Here we show how the coupling of spatial and temporal information inside a multi-mode fiber (MMF) can be harnessed to program generalized measurements for large photonic time-bin qudits. By exciting superpositions of special sets of spatial modes that are temporally unscattered through the fiber, we engineer arbitrary measurements of photon time-bins in dimensions up to 11. The single fiber serves as a scalable, common-path interferometer for time-bin qudits that significantly eases the experimental overheads of standard approaches based on unbalanced Franson-type interferometers.
The field of high-dimensional quantum photonics involves the use of multimode photonic degrees-of-freedom such as the spatial, temporal, or spectral structure of light to encode multi-level quantum states. Recent years have seen rapid progress in the development of methods to generate, manipulate, and distribute such quantum states of light and their use in a range of quantum technology applications that offer practical advantages over conventional qubit-based approaches. High-dimensional quantum states of light encoded in photonic time-bins, frequency-bins, transverse-spatial modes, waveguide paths, and temporal modes have enabled noise-robust fundamental tests of quantum mechanics, error-resilient and high-capacity quantum communication protocols, andas well as efficient approaches for quantum information processing, to name just a few examples. However, research in this field has progressed fairly independently, with little exchange across different photonic degrees-of-freedom or between experiment and theory and no comprehensive comparison between degrees-of-freedom. This roadmap aims to bridge this gap by surveying progress in each area and identifying shared challenges and opportunities that cut across two or more photonic degrees-of-freedoms. We review early work and state-of-the-art experimental techniques under development for high-dimensional quantum states encoded in single and entangled photons, as well as theoretical tools for their measurement and certification. We outline the main outstanding challenges for theory and each experimental degree-of-freedom, identifying promising future directions of research that may enable these to be overcome. We end by discussing interconnections and shared challenges centered around their distribution, measurement, and manipulation, with a view towards their integration into next-generation quantum technology platforms and applications.
Time is a practical and robust degree of freedom for the encoding of quantum information. Qubits encoded in so-called `time-bins', allowing a discrete superposition of two potential arrival times, have their entanglement preserved even over long propagation distances in standard fiber networks [1]. Time has also been used for the preparation of more complex quantum systems, such as hyper-entangled and cluster states [2]. These qualities put time-bin encoding at the center of applications ranging from quantum state preparation through to quantum communications and information processing. One of the hallmarks of the scheme is that a nonlinear element has to be pumped with phase-coherent double-pulses, which can be achieved by using unbalanced interferometers [1], making their phase stability the key determinant of both state generation and analysis accuracy. However, the phase ambiguity arising from the periodicity of feedback signals [3], as well as the difficulty of stabilizing on interference maxima/minima, leave progress to be made in fiberbased interferometry for time-bin encodings.
Single photons are a natural platform for quantum technologies as they support entanglement in many degrees of freedom and are inherently well protected from a detrimental type of noise called decoherence. In order to fully exploit photons for quantum technologies, it will be necessary to be able to shape, control, and measure their properties in all degrees of freedom: space, time, frequency, and polarization. \n \n The time-frequency degree of freedom of light is of particular interest for quantum information tasks as it supports various encodings, including frequency bins and time bins, and is intrinsically robust for propagation through long-distance fibre links. Applications which harness quantum correlations in this degree of freedom, referred to as energy-time entanglement, include dispersion cancellation and high-dimensional quantum key distribution. However, detection of this entanglement and observation of these effects requires time resolution beyond the capabilities of current photon detectors. Thus, for operations on ultrafast time scales, more powerful and complex methods are required. \n \n In this thesis, we use a nonlinear technique known as optical gating to surpass the limitations in current detectors and measure single photon pairs, improving the time resolution by two orders of magnitude. When a single photon enters a nonlinear medium at the same time as a strong laser pulse, it may upconvert to a higher energy photon. The strong laser pulse effectively acts as an ultrafast shutter or gate and this creates a high resolution snapshot of the photon in time. Optical gating in conjunction with single photon spectrometers then allow us to measure both the spectral and temporal features of photons on subpicosecond time scales. \n \n These high resolution measurements enable us to explore a host of quantum effects which remained previously inaccessible. First, we directly observe energy-time entanglement, analogous to Einstein-Rosen-Podolsky correlations but \\emph{in frequency and time}. Then, with full control over the dispersion of each photon, we observe nonlocal dispersion cancellation on femtosecond time scales. We also explore ultrafast interferometry in the quantum domain by temporally resolving two-photon interference from a Franson interferometer and observe a violation of the CHSH-Bell inequality. Finally, we show that, using these measurements, it is possible to reconstruct a two-photon energy-time entangled state. Such measurement capabilities will be essential to precisely control both the spectral and temporal shape of entangled photons and to develop new applications in quantum state engineering.