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

Quantum Information and Measurement (QIM)

Probing the measurement process in DTQW via recurrence

Thomas Nitsche, Regina Kruse, Linda Sansoni, M. Štefaňák, T. Kiss, Igor Jex, Sonja Barkhofen, Christine Silberhorn

Published Jan 1, 2017• 0 citations
Publisher

Abstract

The measurement process plays a crucial role in quantum mechanics as it interrupts the unitary evolution of a state. The consequences are apparent when investigating the return probability (Polya-number) of a particle in a Hadamard walk on the line [1,2]: Depending on whether the evolution is restarted or continued after the measurement, either a transient or a recurrent evolution can be observed. We investigate both cases experimentally for the first time by introducing sinks in a time-multiplexed quantum walk setup using a fast-switching electro-optic modulator (EOM). Monitoring the evolution of the walker over 39 steps reveals the fundamental differences of the two cases as predicted by theory: In the restart-regime, the Polya-number will gradually approach unity. In contrast, the continue-regime yields an asymptotic value of the Polya-number of 2/π, which is reached in good approximation after only four steps and then remains almost constant.

DOI
10.1364/qim.2017.qt5a.5

Related papers

Probing the measurement process in DTQW via recurrence

Thomas Nitsche, Regina Kruse, Linda Sansoni +5 more

The measurement process plays a crucial role in quantum mechanics as it interrupts the unitary evolution of a state. The consequences are apparent when investigating the return probability (Polya-number) of a particle in a Hadamard walk on the line [1, 2]: Depending on whether the evolution is restarted or continued after the measurement, either a transient or a recurrent evolution can be observed. We investigate both cases experimentally for the first time and monitor the evolution of the walker over 39 steps, revealing the fundamental differences of the two cases as predicted by theory: In the restart-regime, the Polya-number will gradually approach 1. In contrast, the continue-regime yields an asymptotic value of 2/π.

Conference on Lasers and Electro-Optics•Jan 1, 2017•0 citations

Probing measurement-induced effects in quantum walks via recurrence

Thomas Nitsche, Sonja Barkhofen, Regina Kruse +7 more

Measurements on a quantum particle unavoidably affect its state, since the otherwise unitary evolution of the system is interrupted by a nonunitary projection operation. To probe measurement-induced effects in the state dynamics using a quantum simulator, the challenge is to implement controlled measurements on a small subspace of the system and continue the evolution from the complementary subspace. A powerful platform for versatile quantum evolution is represented by photonic quantum walks because of their high control over all relevant parameters. However, measurement-induced dynamics in such a platform have not yet been realized. We implement controlled measurements in a discrete-time quantum walk based on time-multiplexing. This is achieved by adding a deterministic outcoupling of the optical signal to include measurements constrained to specific positions resulting in the projection of the walker's state on the remaining ones. With this platform and coherent input light, we experimentally simulate measurement-induced single-particle quantum dynamics. We demonstrate the difference between dynamics with only a single measurement at the final step and those including measurements during the evolution. To this aim, we study recurrence as a figure of merit, that is, the return probability to the walker's starting position, which is measured in the two cases. We track the development of the return probability over 36 time steps and observe the onset of both recurrent and transient evolution as an effect of the different measurement schemes, a signature which only emerges for quantum systems. Our simulation of the observed one-particle conditional quantum dynamics does not require a genuine quantum particle but is demonstrated with coherent light.

arXiv:1803.04712•Science Advances•Jun 1, 2018•48 citations

Unmonitored and monitored recurrence in single-photon quantum walks

Xiao-Xiao Chen, Yajing Wang, An‐Ning Zhang +4 more

Recurrence is an interesting property that describes whether the walker will eventually return to the origin on infinite lattices in classical random walks. Since measurement collapse affects the wave function of the walker, in the quantum case, there are two schemes for studying recurrence properties in quantum walks (QWs) depending on how the measurement process is described. One involves restarting after measurements, known as unmonitored measurements, while the other entails monitoring after each step, referred to as monitored measurements. In this paper, we utilize the dependence of recurrence probabilities on the coin parameter to construct biased-coin QWs on a line and investigate the recurrence properties of both schemes. Based on the bulk-optics framework and using a single-photon source, we experimentally demonstrate the distinct recurrence behaviors resulting from the different evolution processes of the walker in the two schemes. This work showcases diverse recurrence properties in single-particle QW systems, thereby enhancing our understanding of measurement-induced recurrence.

Physical Review A•Jul 15, 2024•5 citations

The role of measurement in the recurrence property of discrete timed quantum walks

L. Kecskés, T. Kiss, M. Štefaňák +1 more

The quantum mechanical generalisation of random walks (called Quantum Walks) present us with a broader spectrum of possibilities compared to their classical counterparts. The aim of the presented study is to explore a new portion of this area by incorporating a new step in the process of the Quantum Walk unique to quantum mechanics: the measurement. Our focus lies in the characterising number of the recurrence behaviour of the walk (Polya-number). We observe the effect of the standard projective measurement, a yes-no measurement on the origin and the effect of different measurement schemes (periodic and random) on the definition and the numeric value of the Polya-number.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Apr 29, 2011•0 citations

Quantum state revivals in quantum walks on cycles

Phillip R. Dukes

Recurrence in the classical random walk is well known and described by the Pólya number. For quantum walks, recurrence is similarly understood in terms of the probability of a localized quantum walker to return to its origin. Under certain circumstances the quantum walker may also return to an arbitrary initial quantum state in a finite number of steps. Quantum state revivals in quantum walks on cycles using coin operators which are constant in time and uniform across the path have been described before but only incompletely. In this paper we find the general conditions for which full-quantum state revival will occur.

arXiv:1405.7345•Results in Physics•Jan 1, 2014•33 citations

Pólya number of the continuous-time quantum walks

Z. Darázs, T. Kiss

We propose a definition for the P\'olya number of continuous-time quantum walks to characterize their recurrence properties. The definition involves a series of measurements on the system, each carried out on a different member from an ensemble in order to minimize the disturbance caused by it. We examine various graphs, including the ring, the line, the higher-dimensional integer lattices, and a number of other graphs, and we calculate their P\'olya number. For the timing of the measurements, a Poisson process as well as regular timing are discussed. We find that the speed of decay for the probability at the origin is the key for recurrence.

arXiv:1004.5286•Physical Review A•Jun 16, 2010•22 citations
The measurement process plays a crucial role in quantum mechanics as it interrupts the unitary evolution of a state. The consequences are apparent when investigating the return probability (Polya-number) of a particle in a Hadamard walk on the line [1,2]: Depending on whether the evolution is restarted or continued after the measurement, either a transient or a recurrent evolution can be observed. We investigate both cases experimentally for the first time by introducing sinks in a time-multiplexed quantum walk setup using a fast-switching electro-optic modulator (EOM). Monitoring the evolution of the walker over 39 steps reveals the fundamental differences of the two cases as predicted by theory: In the restart-regime, the Polya-number will gradually approach unity. In contrast, the continue-regime yields an asymptotic value of the Polya-number of 2/π, which is reached in good approximation after only four steps and then remains almost constant.
The measurement process plays a crucial role in quantum mechanics as it interrupts the unitary evolution of a state. The consequences are apparent when investigating the return probability (Polya-number) of a particle in a Hadamard walk on the line [1, 2]: Depending on whether the evolution is restarted or continued after the measurement, either a transient or a recurrent evolution can be observed. We investigate both cases experimentally for the first time and monitor the evolution of the walker over 39 steps, revealing the fundamental differences of the two cases as predicted by theory: In the restart-regime, the Polya-number will gradually approach 1. In contrast, the continue-regime yields an asymptotic value of 2/π.
Measurements on a quantum particle unavoidably affect its state, since the otherwise unitary evolution of the system is interrupted by a nonunitary projection operation. To probe measurement-induced effects in the state dynamics using a quantum simulator, the challenge is to implement controlled measurements on a small subspace of the system and continue the evolution from the complementary subspace. A powerful platform for versatile quantum evolution is represented by photonic quantum walks because of their high control over all relevant parameters. However, measurement-induced dynamics in such a platform have not yet been realized. We implement controlled measurements in a discrete-time quantum walk based on time-multiplexing. This is achieved by adding a deterministic outcoupling of the optical signal to include measurements constrained to specific positions resulting in the projection of the walker's state on the remaining ones. With this platform and coherent input light, we experimentally simulate measurement-induced single-particle quantum dynamics. We demonstrate the difference between dynamics with only a single measurement at the final step and those including measurements during the evolution. To this aim, we study recurrence as a figure of merit, that is, the return probability to the walker's starting position, which is measured in the two cases. We track the development of the return probability over 36 time steps and observe the onset of both recurrent and transient evolution as an effect of the different measurement schemes, a signature which only emerges for quantum systems. Our simulation of the observed one-particle conditional quantum dynamics does not require a genuine quantum particle but is demonstrated with coherent light.
Recurrence is an interesting property that describes whether the walker will eventually return to the origin on infinite lattices in classical random walks. Since measurement collapse affects the wave function of the walker, in the quantum case, there are two schemes for studying recurrence properties in quantum walks (QWs) depending on how the measurement process is described. One involves restarting after measurements, known as unmonitored measurements, while the other entails monitoring after each step, referred to as monitored measurements. In this paper, we utilize the dependence of recurrence probabilities on the coin parameter to construct biased-coin QWs on a line and investigate the recurrence properties of both schemes. Based on the bulk-optics framework and using a single-photon source, we experimentally demonstrate the distinct recurrence behaviors resulting from the different evolution processes of the walker in the two schemes. This work showcases diverse recurrence properties in single-particle QW systems, thereby enhancing our understanding of measurement-induced recurrence.
The quantum mechanical generalisation of random walks (called Quantum Walks) present us with a broader spectrum of possibilities compared to their classical counterparts. The aim of the presented study is to explore a new portion of this area by incorporating a new step in the process of the Quantum Walk unique to quantum mechanics: the measurement. Our focus lies in the characterising number of the recurrence behaviour of the walk (Polya-number). We observe the effect of the standard projective measurement, a yes-no measurement on the origin and the effect of different measurement schemes (periodic and random) on the definition and the numeric value of the Polya-number.
Recurrence in the classical random walk is well known and described by the Pólya number. For quantum walks, recurrence is similarly understood in terms of the probability of a localized quantum walker to return to its origin. Under certain circumstances the quantum walker may also return to an arbitrary initial quantum state in a finite number of steps. Quantum state revivals in quantum walks on cycles using coin operators which are constant in time and uniform across the path have been described before but only incompletely. In this paper we find the general conditions for which full-quantum state revival will occur.
We propose a definition for the P\'olya number of continuous-time quantum walks to characterize their recurrence properties. The definition involves a series of measurements on the system, each carried out on a different member from an ensemble in order to minimize the disturbance caused by it. We examine various graphs, including the ring, the line, the higher-dimensional integer lattices, and a number of other graphs, and we calculate their P\'olya number. For the timing of the measurements, a Poisson process as well as regular timing are discussed. We find that the speed of decay for the probability at the origin is the key for recurrence.