Measuring the classical and quantum states and ultrafast correlations of optical fields

Matan Even Tzur, Chen Mor, Noa Yaffe +8 more

The generation and control of extreme ultraviolet (XUV) radiation by high harmonic generation (HHG) have advanced ultrafast science, providing direct insights into electron dynamics on their natural time scale. Attosecond science has established the capability to resolve ultrafast quantum phenomena in matter by characterizing and controlling the classical properties of the high harmonics. Recent theoretical proposals have introduced novel schemes for generating and manipulating XUV HHG with distinct quantum features, paving the way to attosecond quantum optics. In this work, we transfer fundamental concepts in quantum optics into attosecond science. By driving the HHG process with a combination of an infrared bright squeezed vacuum (BSV, a non-classical state of light), and a strong coherent field, we imprint the quantum correlations of the input BSV onto both the ultrafast electron wavefunction and the harmonics' field. Performing in-situ HHG interferometry provides an insight into the underlying sub-cycle dynamics, revealing squeezing in the statistical properties of one of the most fundamental strong-field phenomena -- field induced tunneling. Our measurement allows the reconstruction of the quantum state of the harmonics through homodyne-like tomography, resolving correlated fluctuations in the harmonic field that mirror those of the input BSV. By controlling the delay between the two driving fields, we manipulate the photon statistics of the emitted attosecond pulses with sub-cycle accuracy. The ability to measure and control quantum correlations in both electrons and XUV attosecond pulses establishes a foundation for attosecond electrodynamics, manipulating the quantum state of electrons and photons with sub-cycle precision.

J. Clausen, Mohammed Dakna, L. Knöll +1 more

Jean-Philippe W. MacLean, Sacha Schwarz, Kevin J. Resch

The generation of ultrafast laser pulses and the reconstruction of their electric fields is essential for many applications in modern optics. Quantum optical fields can also be generated on ultrafast timescales; however, the tools and methods available for strong laser pulses are not appropriate for measuring the properties of weak, possibly entangled pulses. Here, we demonstrate a method to reconstruct the joint-spectral amplitude of a two-photon energy-time entangled state from joint measurements of the frequencies and arrival times of the photons, and the correlations between them. Our reconstruction method is based on a modified Gerchberg-Saxton algorithm. Such techniques are essential to measure and control the shape of ultrafast entangled photon pulses.

Rakesh Kumar

Rupamanjari Ghosh

Zhangyu Zhou, Shuoshuo Zhang, Jielei Ni +5 more

As structured optical fields with spatially inhomogeneous polarization distributions, vector beams have attracted widespread attention for their great applications across multiple fields. The coupling between spatial modes and polarization states in vector beams results in nonseparability analogous to quantum entangled states, referred to as classical entanglement. This concept has garnered considerable scholarly interest, due to its capacity to facilitate quantum-inspired approaches for the characterization of vector optical fields, leading to noteworthy applications such as metrological sensing, communication encryption, and quantum computing. However, most investigations concerning classical entanglement have focused on vector optical fields within the spatial domain, while the classical entanglement characteristics of ultrafast vector beam pulses in the temporal domain remain to be revealed. Here, we investigate the classical local entanglement of ultrafast vector beam pulses in the temporal domain. Through theoretical interpretation and experimental verification, time-varying nonseparability has been demonstrated throughout the pulse duration. The dynamic evolution of spatially vectorial polarization states on femtosecond timescales was measured. The temporal evolution of the classical entanglement and the associated density matrix were analyzed using quantum state tomography. This research provides, to our knowledge, novel perspectives for investigating quantum-classical optical analogies in the temporal domain, advancing deeper fundamental understanding of entanglement.