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Journal of Spectroscopy

Investigation of the Time Behavior of the Second-Order Coherence Function of a Tunable Single-Photon Source

Azadeh Ahmadian, Rasoul Malekfar

Published Jun 2, 2021• 0 citations
Publisher

Abstract

Single-photon sources are critical optical components in quantum communication, in particular, for security applications. One of the essential parameters that define these sources is the magnitude of the second-order coherence function, whose investigation reveals the state of the emitted photon. In this study, we indicate that the second-order coherence function varies over time when using two lasers and preparing coherent population trapping. The calculation is based on solving the master equation to find the density matrix corresponding to the emission dynamics and provide the second-order coherence function. The changes of the second-order coherence function can be estimated and the system behavior regarding photon emission can be predicted by solving the master equation based on the parameters obtained from the experimental results of a nitrogen vacancy (NV) in a diamond. Here we report, for the first time to the best of our knowledge, that the state of the emitted photons persists in the strong interaction of the aforementioned process. As using two lasers is a familiar method for controlling the single-photon source and the stability of the source is an essential point in a quantum network, this study can be considered to develop quantum network components such as memory and on-demand single-photon sources. Also, it suggests a method for tuning photon statistics while controlling the photon states.

DOI
10.1155/2021/8811424

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Single-photon sources are critical optical components in quantum communication, in particular, for security applications. One of the essential parameters that define these sources is the magnitude of the second-order coherence function, whose investigation reveals the state of the emitted photon. In this study, we indicate that the second-order coherence function varies over time when using two lasers and preparing coherent population trapping. The calculation is based on solving the master equation to find the density matrix corresponding to the emission dynamics and provide the second-order coherence function. The changes of the second-order coherence function can be estimated and the system behavior regarding photon emission can be predicted by solving the master equation based on the parameters obtained from the experimental results of a nitrogen vacancy (NV) in a diamond. Here we report, for the first time to the best of our knowledge, that the state of the emitted photons persists in the strong interaction of the aforementioned process. As using two lasers is a familiar method for controlling the single-photon source and the stability of the source is an essential point in a quantum network, this study can be considered to develop quantum network components such as memory and on-demand single-photon sources. Also, it suggests a method for tuning photon statistics while controlling the photon states.
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Photon interference among distant quantum emitters is a promising method to generate large scale quantum networks. Interference is best achieved when photons show long coherence times. For the nitrogen-vacancy defect center in diamond we measure the coherence times of photons via optically induced Rabi oscillations. Experiments reveal a close to Fourier-transform (i.e., lifetime) limited width of photons emitted even when averaged over minutes. The projected contrast of two-photon interference (0.8) is high enough to envisage applications in quantum information processing. We report 12 and 7.8 ns excited state lifetimes depending on the spin state of the defect.
Photon interference among distant quantum emitters is a promising method to generate large scale quantum networks. Interference is best achieved when photons show long coherence times. For the nitrogen-vacancy defect center in diamond we measure the coherence times of photons via optically induced Rabi oscillations. Experiments reveal a close to Fourier transform (i.e. lifetime) limited width of photons emitted even when averaged over minutes. The projected contrast of two-photon interference (0.8) is high enough to envisage the applications in quantum information processing. We report 12 and 7.8 ns excited state lifetime depending on the spin state of the defect.
Estimating the quality of a single-photon source is crucial for its use in quantum technologies. The standard test for semiconductor sources is a value of the second-order correlation function of the emitted field below 1/21/21/2 at zero time delay. This criterion alone provides no information regarding the amplitude of the single-photon contribution for general quantum states. Addressing this question requires the knowledge of additional observables. We derive an effective second-order correlation function, strongly connected to the Mandel-QQQ parameter and given in terms of both the second-order correlation and the average photon number, that provides a lower bound on the single-to-multiphoton projection ratio. Using both observables individually allows for lower and upper bounds for the single-photon projection. Comparing the tightness of our bounds with those in the literature, we find that relative bounds may be better described using the average photon number, while absolute bounds for low excitation states are tighter using the vacuum projection. Our results show that estimating the quality of a single-photon source based on additional information is very much dependent on what aspect of the quantum state of light one is interested in.
We propose and demonstrate a method for an independent verification of a degree of single photon purity and coherence applicable for all single-photon emitters used in pulsed mode. Using two-time second-order correlation measurements, we reconstruct the dynamics of the nonclassical photon wavepacket. This reveals the temporal evolution of the photon field during the excitation-relaxation cycle of an emitter. The technique allows for the simultaneous measurement of multiphoton content and decoherence. Here we applied this technique to characterize a nonclassical state produced from a single InAs quantum dot (QD). We experimentally observe variations in the degree of multiphoton content and coherence of the wavepacket. A rate equation is introduced to explain multiphoton variations of our source and is found to describe the observed two-dimensional second-order correlation function accurately.