The generation of entangled states through spontaneous parametric down-conversion (SPDC) is a fundamental process in quantum optics and has practical applications in controlled generation of entangled states. Understanding the influence of pump coherence on the entanglement produced in SPDC is crucial for both theoretical understanding and practical implementation. It is known that the pump coherence in a specific degree of freedom (DOF) sets an upper limit on the generated entanglement in the same DOF when postselection is not applied. However, the cross-influence of pump coherence on the generated entanglement in a different DOF remains poorly understood. In this study, conducted by Cheng Li, Boris Braverman, Girish Kulkarni, and Robert W. Boyd, the researchers experimentally investigate the effect of using a spatiotemporally highly-incoherent (STHI) light-emitting diode (LED) pump on polarization entanglement generated in SPDC. The choice to use an STHI source as a pump is motivated by its ubiquity and wider range of available wavelengths compared to lasers. To assess the impact of STHI pumps on polarization entanglement, quantum state tomography measurements are performed using multimode collection fibers to minimize postselection effects. The experimental results reveal that the output polarization two-qubit state exhibits reduced entanglement and purity when an STHI pump is used. Specifically, a concurrence value of 0.531+/-0.006 and a purity value of 0.647+/-0.005 are obtained, which closely align with the theoretically predicted values of 0.536 for concurrence and 0.643 for purity. Despite observing reduced entanglement and purity with STHI pumps, this study highlights two important reasons why SPDC with STHI pumps remains valuable: First, STHI sources are readily available at various wavelengths, making them more accessible than lasers. Second, the polarization-entangled two-photon states generated using STHI pumps exhibit robustness to scattering, suggesting potential utility in long-distance quantum communication schemes. In summary, this research provides experimental insights into the influence of pump coherence on polarization entanglement generated through SPDC.
Spontaneous parametric down-conversion (SPDC) is a process in quantum optics where light particles split into pairs. Entangled states are created using SPDC, which has practical uses. The quality of the entanglement depends on how well the original light source is organized. Researchers are studying how different types of light sources affect the entanglement. They found that using a certain type of light-emitting diode (LED) reduces the quality of the entanglement compared to what was expected. However, using this type of LED is still useful because it is easier to get and can be used for long-distance communication."
Definitions
- Spontaneous parametric down-conversion (SPDC): A process in quantum optics where light particles split into pairs.
- Entangled states: States where two or more particles are connected and their properties are linked.
- Coherence: How well organized or structured something is.
- Degree of freedom (DOF): A specific aspect or characteristic that can change independently.
- Postselection: Choosing only certain results after an experiment has been done.
- Spatiotemporally highly-incoherent (STHI): Light that is not organized or structured in space and time.
- Light-emitting diode (LED): A device that emits light when an electric current passes through it.
- Polarization entanglement: Entanglement based on the polarization direction of light particles.
- Quantum state tomography: Measuring and characterizing the properties of
Understanding the Impact of Pump Coherence on Entanglement Generated Through Spontaneous Parametric Down-Conversion
Spontaneous parametric down-conversion (SPDC) is a fundamental process in quantum optics and has practical applications in controlled generation of entangled states. Understanding the influence of pump coherence on the entanglement produced in SPDC is crucial for both theoretical understanding and practical implementation. In this study, conducted by Cheng Li, Boris Braverman, Girish Kulkarni, and Robert W. Boyd, researchers experimentally investigate the effect of using a spatiotemporally highly-incoherent (STHI) light-emitting diode (LED) pump on polarization entanglement generated in SPDC.
Background Information
It is known that the pump coherence in a specific degree of freedom (DOF) sets an upper limit on the generated entanglement in the same DOF when postselection is not applied. However, cross-influence between pump coherence and generated entanglement in different DOFs remains poorly understood. The choice to use an STHI source as a pump was motivated by its ubiquity and wider range of available wavelengths compared to lasers.
Experimental Design
To assess the impact of STHI pumps on polarization entanglement, quantum state tomography measurements were performed using multimode collection fibers to minimize postselection effects. The experimental results revealed that output polarization two-qubit state exhibited reduced entanglement and purity when an STHI pump was used; specifically concurrence value 0.531+/-0.006 was obtained along with a purity value 0f 0647+/-0.005 which closely aligns with theoretically predicted values: 0.536 for concurrence and 0643 for purity respectively .
Conclusion & Implications
Despite observing reduced entanglement and purity with STHI pumps, this study highlights two important reasons why SPDC with STHI pumps remain valuable: First, they are readily available at various wavelengths making them more accessible than lasers; second they exhibit robustness to scattering suggesting potential utility in long distance quantum communication schemes . This research provides experimental insights into influence of pump coherence on polarization entanglements generated through SPDC
The influence of pump coherence on the entanglement produced in spontaneous parametric down-conversion (SPDC) is important to understand, both from a fundamental perspective, and from a practical standpoint for controlled generation of entangled states. In this context, it is known that in the absence of postselection, the pump coherence in a given degree of freedom (DOF) imposes an upper limit on the generated entanglement in the same DOF. However, the cross-influence of the pump coherence on the generated entanglement in a different DOF is not well-understood. Here, we experimentally investigate the effect of a spatiotemporally highly-incoherent (STHI) light-emitting diode (LED) pump on the polarization entanglement generated in SPDC. Our quantum state tomography measurements using multimode collection fibers to reduce the influence of postselection yield a two-qubit state with a concurrence of 0.531+/-0.006 and a purity of 0.647+/-0.005, in excellent agreement with our theoretically predicted concurrence of 0.536 and purity of 0.643. Therefore, while the use of an STHI pump causes reduction in the entanglement and purity of the output polarization two-qubit state, the viability of SPDC with STHI pumps is nevertheless important for two reasons: (i) STHI sources are ubiquitous and available at a wider range of wavelengths than lasers, and (ii) the generated STHI polarization-entangled two-photon states could potentially be useful in long-distance quantum communication schemes due to their robustness to scattering.
