In a parametric down-conversion process pumped by chirped femtosecond pulses, we produce high-intensity near-infrared twin beams with a sub-4-cycle pulse duration, high occupancy of the fundamental temporal mode and strong photon-number correlations. These pulses are well-positioned for the implementation of bright squeezed states as the probe in electro-optic sampling, toward the accurate detection of non-Gaussian quantum fields in the terahertz-to-mid-infrared spectral range.
In a parametric down-conversion process pumped by chirped femtosecond pulses, we produce high-intensity near-infrared twin beams with a sub-4-cycle pulse duration, high occupancy of the fundamental temporal mode and strong photon-number correlations. These pulses are well-positioned for the implementation of bright squeezed states as the probe in electro-optic sampling, toward the accurate detection of non-Gaussian quantum fields in the terahertz-to-mid-infrared spectral range.
A time-domain approach to quantum electrodynamics is presented, covering the entire mid-infrared and terahertz frequency ranges. Ultrabroadband electro-optic sampling with few-femtosecond laser pulses allows direct detection of the vacuum fluctuations of the electric field in free space [1,2]. Besides the Planck and electric field fundamental constants, the variance of the ground state is determined solely by the inverse of the four-dimensional space-time volume over which a measurement or physical process integrates. Therefore, we can vary the contribution of multi-terahertz vacuum fluctuations and discriminate against the trivial shot noise due to the constant flux of near-infrared probe photons. Subcycle temporal resolution based on a nonlinear phase shift provides signals from purely virtual photons for accessing the ground-state wave function without amplification to finite intensity. Recently, we have succeeded in generation and analysis of mid-infrared squeezed transients with quantum noise patterns that are time-locked to the intensity envelope of the probe pulses. We find subcycle temporal positions with a noise level distinctly below the bare vacuum which serves as a direct reference. Delay times with increased differential noise indicate generation of highly correlated quantum fields by spontaneous parametric fluorescence. Our time-domain approach offers a generalized understanding of spontaneous emission processes as a consequence of local anomalies in the co-propagating reference frame modulating the quantum vacuum, in combination with the boundary conditions set by Heisenberg’s uncertainty principle. [1] C. Riek et al., Science 350, 420 (2015) [2] A. S. Moskalenko et al., Phys. Rev. Lett. 115, 263601 (2015)
We introduce an ultrafast, bright, entangled twin-beam source generated by type-0 parametric down-conversion in periodically-poled lithium niobate at MHz repetition rate, with continuously tunable Schmidt number K set by the pump pulse duration. Photon-number statistics characterization via g(2)(0) and singular-value decomposition of the signal spectral density matrix yield K≃1.05 and K≃1.03, respectively, maintained over multiple orders of magnitude in brightness. Group-delay dispersion of the pump drives a continuous transition from single-mode operation to a controlled multimode regime, consistent with the temporal gain window departing from the inverse phase-matching bandwidth. Strong non-degeneracy of the source (signal at 1.37 um, idler at 4.0 um, ∼100 fs duration) decouples a mid-infrared interaction wavelength, which overlaps with molecular vibrational resonances, from a near-infrared detection band, establishing a practical platform for quantum-enhanced metrology, nonlinear interferometry, and mid-infrared spectroscopic sensing. We show that in the bright few-mode limit, the total entanglement resource is clearly separated between modal and occupational degrees of freedom, and that our source allocates up to 95-97% of that resource to the occupational sector.
Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume of V T H z ∼ 10 − 9 ( λ T H z / 2 ) 3 in combination with ultraperformant organic molecules ( r 33 = 170 p m / V ) and accomplish a record-high single-photon electro-optic coupling rate of g e o = 2 π × 0.043 G H z , 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is C 0 = 1.6 × 10 − 8 , and the multiphoton cooperativity is C = 0.002 at room temperature. We show > 70 d B dynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.
We introduce an ultrafast, bright, entangled twin-beam source generated by type-0 parametric down-conversion in periodically-poled lithium niobate at MHz repetition rate, with continuously tunable Schmidt number K set by the pump pulse duration. Photon-number statistics characterization via g(2)(0) and singular-value decomposition of the signal spectral density matrix yield K ~ 1.05 and K ~ 1.03, respectively, maintained over multiple orders of magnitude in brightness. Group-delay dispersion of the pump drives a continuous transition from single-mode operation to a controlled multimode regime, consistent with the temporal gain window departing from the inverse phase-matching bandwidth. Strong non-degeneracy of the source (signal at 1.37 µm, idler at 4.0 µm, ~ 100 fs duration) decouples a mid-infrared interaction wavelength, which overlaps with molecular vibrational resonances, from a near-infrared detection band, establishing a practical platform for quantum-enhanced metrology, nonlinear interferometry, and mid-infrared spectroscopic sensing. We show that in the bright few-mode limit, the total entanglement resource is clearly separated between modal and occupational degrees of freedom, and that our source allocates up to 95-97% of that resource to the occupational sector.
We introduce an ultrafast, bright, entangled twin-beam source generated by type-0 parametric down-conversion in periodically-poled lithium niobate at MHz repetition rate, with continuously tunable Schmidt number K set by the pump pulse duration. Photon-number statistics characterization via g(2)(0) and singular-value decomposition of the signal spectral density matrix yield K ~ 1.05 and K ~ 1.03, respectively, maintained over multiple orders of magnitude in brightness. Group-delay dispersion of the pump drives a continuous transition from single-mode operation to a controlled multimode regime, consistent with the temporal gain window departing from the inverse phase-matching bandwidth. Strong non-degeneracy of the source (signal at 1.37 µm, idler at 4.0 µm, ~ 100 fs duration) decouples a mid-infrared interaction wavelength, which overlaps with molecular vibrational resonances, from a near-infrared detection band, establishing a practical platform for quantum-enhanced metrology, nonlinear interferometry, and mid-infrared spectroscopic sensing. We show that in the bright few-mode limit, the total entanglement resource is clearly separated between modal and occupational degrees of freedom, and that our source allocates up to 95-97% of that resource to the occupational sector.