Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced SPDC (original) (raw)
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Nature Photonics, 2011
The preparation and storage of photonic entanglement are central to the achievement of scalable linear optical quantum computation (LOQC). The most widely used photonic entanglement source (a spontaneous parametric downconversion (SPDC) source) is not directly suitable for storage, because its working frequency bandwidth is significantly larger than any available quantum memory. To remedy this problem, cavity-enhanced narrow-band SPDC sources have been developed. However, the storage of cavity-enhanced narrow-band entangled photons has not yet been achieved. Also, the spectral correlations between the entangled photons can make them practically useless for scalable LOQC. Here, we report the preparation and storage of frequency-uncorrelated narrowband (5 MHz) entangled photons from a cavity-enhanced SPDC source. The frequency correlation between the entangled photons is eliminated by changing the continuous UV pumping beam to short pulses. The storage of the polarization state of a single photon, and of a photon entangled with another flying in the fibre, is demonstrated. Our work demonstrates a quantum interface between narrow-band entangled photons from cavity SPDC and atomic quantum memory, and thus provides an important tool towards the achievement of all-optical quantum information processing.
Generation of Narrow-Band Polarization-Entangled Photon Pairs for Atomic Quantum Memories
Physical Review Letters, 2008
We report an experimental realization of a narrow-band polarization-entangled photon source with a linewidth of 9.6 MHz through cavity-enhanced spontaneous parametric down-conversion. This linewidth is comparable to the typical linewidth of atomic ensemble based quantum memories. Single-mode output is realized by setting a reasonable cavity length difference between different polarizations, using of temperature controlled etalons and actively stabilizing the cavity. The entangled property is characterized with quantum state tomography, giving a fidelity of 94% between our state and a maximally entangled state. The coherence length is directly measured to be 32 m through two-photon interference.
A SPDC-Based Source of Entangled Photons and its Characterization
Journal of Russian Laser Research, 2015
We present a short review of development and applications of single and biphoton sources. The main emphasis is on spontaneous parametric down-conversion (SPDC) sources capable of producing timecorrelated photon pairs. We also present a SPDC source of photon pairs at 1,064 nm pumped by a cw 532 nm laser. We consider the fundamental principles of quantum tomography and present results of characterization (entanglement and purity) of biphoton quantum states produced by this source. Additionally, we discuss some aspects of quantum entanglement suppression caused by the Migdall effect in a double-crystal scheme.
Tunable control of the frequency correlations of entangled photons
Optics Letters, 2007
We demonstrate experimentally a new technique to control the bandwidth and the type of frequency correlations (correlation, anticorrelation, and even uncorrelation) of entangled photons generated by spontaneous parametric downconversion. The method is based on the control of the group velocities of the interacting waves. This technique can be applied in any nonlinear medium and frequency band of interest. It is also demonstrated that this technique helps enhance the quality of polarization entanglement even when femtosecond pulses are used as a pump.
arXiv: Atomic Physics, 2020
We interface a spontaneous parametric down conversion (SPDC) crystal and a cold atomic ensemble and demonstrate a highly efficient quantum memory through polarization-encoded single-photon qubits. Specifically, narrowband heralded single photons from a cavity-enhanced SPDC source is stored using cold atomic ensemble, with ~70% storage-and-retrieval efficiency and ~10$\mu$s storage time at 50% efficiency. To prevent the degradation after storage, we also manipulate the single-photon wave profile so that the retrieved non-classical nature of single photon is preserved. On the other hand, the dual-rail storage is used for storing polarization-encoded qubits, and the corrected fidelity of flying qubits after storage reaches ~97%. The results pave the way toward large-scale quantum network.
Polarization-entanglement-conserving frequency conversion of photons
Physical Review A, 2012
Entangled photons play a pivotal role in the distribution of quantum information in quantum networks. However, the frequency bands for optimal transmission and storage of photons are not necessarily the same. Here we experimentally demonstrate the coherent frequency conversion of photons entangled in their polarization, a widely used degree of freedom in photonic quantum information processing. We verify the successful entanglement conversion by violating a Clauser-Horne-Shimony-Holt (CHSH) Bell inequality and fully confirm that our characterised fidelity of entanglement transfer is close to unity using both state and process tomography. Our implementation is robust and flexible, making it a practical building block for future quantum networks.
Tunable Control of the Bandwidth and Frequency Correlations of Entangled Photons
2007
We demonstrate experimentally a new technique to control the bandwidth and the type of frequency correlations (correlation, anticorrelation, and even uncorrelation) of entangled photons generated by spontaneous parametric downconversion. The method is based on the control of the group velocities of the interacting waves. This technique can be applied in any nonlinear medium and frequency band of interest. It is also demonstrated that this technique helps enhance the quality of polarization entanglement even when femtosecond pulses are used as a pump.