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Amplitude and phase modulation of time-energy entangled two-photon states

Zäh, Florian, Halder, Matthias, Thomas Feurer

Published Jan 1, 2008• 28 citations
OpenAlex

Abstract

We experimentally demonstrate amplitude and phase modulation of a time-energy entangled two-photon wave function. The entangled photons are produced by spontaneous parametric down-conversion, spectrally dispersed in an prism compressor, modulated in amplitude and/or phase, and detected in coincidence by sum-frequency generation. First, we present a Fourier optical analysis of the optical setup yielding an analytic expression for the resulting field distribution at the exit plane of the shaping apparatus. We then introduce amplitude and/or phase shaping and present results which can only be obtained through a combination of the two. Specifically, we use a shaper-based interferometer to measure the two-photon interference of an almost bandwidth-limited two-photon wave function.

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Amplitude and phase modulation of time-energy entangled two-photon states

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We experimentally demonstrate amplitude and phase modulation of a time-energy entangled two-photon wave function. The entangled photons are produced by spontaneous parametric down-conversion, spectrally dispersed in an prism compressor, modulated in amplitude and/or phase, and detected in coincidence by sum-frequency generation. First, we present a Fourier optical analysis of the optical setup yielding an analytic expression for the resulting field distribution at the exit plane of the shaping apparatus. We then introduce amplitude and/or phase shaping and present results which can only be obtained through a combination of the two. Specifically, we use a shaper-based interferometer to measure the two-photon interference of an almost bandwidth-limited two-photon wave function.

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We demonstrate spectral amplitude and phase modulation of time-energy entangled photon pairs by means of a spatial light modulator (SLM) [1]. Coincidences are detected by sum frequency generation in a nonlinear crystal which has been applied in several experiments as an ultrafast coincidence detection method to temporally resolve entangled photons on a timescale of fs [2,3]. By taking into account the properties of the detection crystal, we derive an expression for the up-converted frequency signal in the form of a second-order correlation function G(1)[3]. This detection scheme is in contrast to a perfect coincidence detection described by the fourth-order correlation function G(2). However, in former two photon shaping experiments [1,2] the detected signal was compared to simulations based on G(2). We investigate here under which conditions the G(2)ceases to provide an accurate description of the measurements.

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We present an experimental and theoretical analysis of the energy-time entanglement properties of a two-photon state generated by pulsed spontaneous parametric down-conversion. Different methods of spectral or temporal shaping of one of the two photons have allowed the observation of nonlocal modulations in the autocorrelation or in the spectrum of the other, by coincidence measurements. Either a monochromator or etalon filters have been used to shape the idler photon while observing the conditioned signal autocorrelation with a Michelson interferometer. Alternatively, the unbalanced interferometer has been used to shape the signal photon while measuring the conditioned idler spectrum with the monochromator. The role of the pump spectrum has been investigated by shaping it with additional filters. A theoretical treatment has allowed us to completely describe all the observed features as a function of the different experimental parameters.

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In spontaneous parametric down-conversion, the spectral correlations between the signal and the idler are expressed by the joint spectral amplitude (JSA) function. However, in the standard coincidence measurements, the phase information of the JSA is lost, and only the square of the absolute value of the JSA is recorded, thus preventing full characterization of the biphoton state. Here, we present an experimental technique to investigate the interference of biphoton joint spectral amplitudes, unlocking new avenues in quantum photonics research. Our method explores phase-dependent phenomena within entangled biphoton spectra. This is achieved by simultaneously pumping two structured nonlinear photonic crystals and observing their interference, which reveals previously inaccessible effects with direct intensity measurements. We demonstrate the versatility of our technique by analyzing two types of joint spectra: one exhibiting a two-lobe shape and the other a three-lobe shape. Additionally, we reconstruct the joint spectral amplitudes for both scenarios and observe good agreement with theoretical predictions. These results pave the way for developing advanced quantum communication and information processing technologies using biphoton spectra.

Optica Quantum•Sep 23, 2024•3 citations
We experimentally demonstrate amplitude and phase modulation of a time-energy entangled two-photon wave function. The entangled photons are produced by spontaneous parametric down-conversion, spectrally dispersed in an prism compressor, modulated in amplitude and/or phase, and detected in coincidence by sum-frequency generation. First, we present a Fourier optical analysis of the optical setup yielding an analytic expression for the resulting field distribution at the exit plane of the shaping apparatus. We then introduce amplitude and/or phase shaping and present results which can only be obtained through a combination of the two. Specifically, we use a shaper-based interferometer to measure the two-photon interference of an almost bandwidth-limited two-photon wave function.
We experimentally demonstrate amplitude and phase modulation of a time-energy entangled two-photon wave function. The entangled photons are produced by spontaneous parametric down-conversion, spectrally dispersed in an prism compressor, modulated in amplitude and/or phase, and detected in coincidence by sum-frequency generation. First, we present a Fourier optical analysis of the optical setup yielding an analytic expression for the resulting field distribution at the exit plane of the shaping apparatus. We then introduce amplitude and/or phase shaping and present results which can only be obtained through a combination of the two. Specifically, we use a shaper-based interferometer to measure the two-photon interference of an almost bandwidth-limited two-photon wave function.
We demonstrate spectral amplitude and phase modulation of time-energy entangled photon pairs by means of a spatial light modulator (SLM) [1]. Coincidences are detected by sum frequency generation in a nonlinear crystal which has been applied in several experiments as an ultrafast coincidence detection method to temporally resolve entangled photons on a timescale of fs [2,3]. By taking into account the properties of the detection crystal, we derive an expression for the up-converted frequency signal in the form of a second-order correlation function G(1)[3]. This detection scheme is in contrast to a perfect coincidence detection described by the fourth-order correlation function G(2). However, in former two photon shaping experiments [1,2] the detected signal was compared to simulations based on G(2). We investigate here under which conditions the G(2)ceases to provide an accurate description of the measurements.
The time-energy entanglement of down-converted photon pairs is particularly difficult to characterize because direct measurements of photon arrival times are limited by the temporal resolution of photon detection. Here, we explore an alternative possibility of characterizing the temporal coherence of two-photon wave functions using single-photon interference with weak coherent light. Specifically, this method makes use of the fact that down conversion generates a coherent superposition of vacuum and two-photon states, so that the coincidence count rates for photon pairs after interference with weak coherent light are given by a superposition of the two-photon wave function from the down conversion with the product wave function defined by the weak coherent references. By observing the frequency-dependent interference pattern, it is possible to reconstruct the amplitudes and the phases of the two-photon wave function within the bandwidth of the reference pulses used in the single-photon interferences. The correlated single-photon interferences therefore provide a direct map of the entangled two-photon wave function generated in the down-conversion process.
We present an experimental and theoretical analysis of the energy-time entanglement properties of a two-photon state generated by pulsed spontaneous parametric down-conversion. Different methods of spectral or temporal shaping of one of the two photons have allowed the observation of nonlocal modulations in the autocorrelation or in the spectrum of the other, by coincidence measurements. Either a monochromator or etalon filters have been used to shape the idler photon while observing the conditioned signal autocorrelation with a Michelson interferometer. Alternatively, the unbalanced interferometer has been used to shape the signal photon while measuring the conditioned idler spectrum with the monochromator. The role of the pump spectrum has been investigated by shaping it with additional filters. A theoretical treatment has allowed us to completely describe all the observed features as a function of the different experimental parameters.
We experimentally demonstrate shaping of the two-photon wave function of entangled-photon pairs, utilizing coherent pulse-shaping techniques. By performing spectral-phase manipulations we tailor the second-order correlation function of the photons exactly like a coherent ultrashort pulse. To observe the shaping we perform sum-frequency generation with an ultrahigh flux of entangled photons. At the appropriate conditions, sum-frequency generation performs as a coincidence detector with an ultrashort response time (approximately 100 fs), enabling a direct observation of the two-photon wave function. This property also enables us to demonstrate background-free, high-visibility two-photon interference oscillations.
In spontaneous parametric down-conversion, the spectral correlations between the signal and the idler are expressed by the joint spectral amplitude (JSA) function. However, in the standard coincidence measurements, the phase information of the JSA is lost, and only the square of the absolute value of the JSA is recorded, thus preventing full characterization of the biphoton state. Here, we present an experimental technique to investigate the interference of biphoton joint spectral amplitudes, unlocking new avenues in quantum photonics research. Our method explores phase-dependent phenomena within entangled biphoton spectra. This is achieved by simultaneously pumping two structured nonlinear photonic crystals and observing their interference, which reveals previously inaccessible effects with direct intensity measurements. We demonstrate the versatility of our technique by analyzing two types of joint spectra: one exhibiting a two-lobe shape and the other a three-lobe shape. Additionally, we reconstruct the joint spectral amplitudes for both scenarios and observe good agreement with theoretical predictions. These results pave the way for developing advanced quantum communication and information processing technologies using biphoton spectra.