Transfer of temporal coherence in parametric down-conversion

Kulkarni, Girish; Kumar, Prashant; Jha, Anand K.

doi:10.1364/josab.34.001637

Cited by 16 publications

(12 citation statements)

References 68 publications

(137 reference statements)

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“…Along similar lines, the influence of different coherent pump profiles on entanglement and on the propagation of the generated pairs have been already explored [19][20][21][22][23]. The impact of temporal coherence of the pump has been investigated in [24][25][26].…”

mentioning

confidence: 99%

Influence of pump coherence on the generation of position-momentum entanglement in optical parametric down-conversion

Zhang¹,

Fickler²,

Giese³

et al. 2019

Opt. Express

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Strong correlations in two conjugate variables are the signature of quantum entanglement and have played a key role in the development of modern physics [1,2]. Entangled photons have become a standard tool in quantum information [3] and foundations [4,5]. An impressive example is position-momentum entanglement of photon pairs [6], explained heuristically through the correlations implied by a common birth zone and momentum conservation. However, these arguments entirely neglect the importance of the 'quantumness', i.e. coherence, of the driving force behind the generation mechanism. We study theoretically and experimentally how the correlations depend on the coherence of the pump of nonlinear down-conversion. In the extreme case -a truly incoherent pump -only position correlations exist. By increasing the pump's coherence, correlations in momenta emerge until their strength is sufficient to produce entanglement. Our results shed light on entanglement generation and can be applied to adjust the entanglement for quantum information applications.Entanglement of photons has been explored among different degrees of freedom, such as polarization [4,5,7], time and frequency [8,9], position and momentum [6] as well as angular position and orbital angular momentum [10,11]. Entanglement of two-dimensional systems, in analogy to classical bits, is the primary resource for quantum communication and processing [3]. In addition, multiple-level quantum systems can show highdimensional entanglement with a high complexity [12][13][14] and can be exploited for various quantum information tasks [15]. Position-momentum entanglement as a continuous degree of freedom is the ultimate limit of highdimensional entanglement and its deeper understanding is essential for the development of novel quantum technologies.Position-momentum-entangled photon pairs can be rather straight-forwardly generated in spontaneous parametric down-conversion (SPDC) [6,16], the workhorse of many quantum optics labs. In this process, a strong pump beam spontaneously generates a pair of signal and idler photons through a nonlinear interaction. Formation of position-momentum entanglement is often explained by simple heuristic arguments: A pump photon is converted at one particular transverse position into signal and idler. Due to this common birth place, they are correlated in position. In addition, transverse momentum conservation requires the generated photons to travel in opposite directions, i.e. they are anti-correlated in momentum. Hence, in an idealized situation the generated pairs can be perfectly correlated in both, the position and momenta, which is the key signature of quantum entanglement. However, these arguments have not taken the coherence properties of the pump beam, i.e. the quantum aspect of the driving force behind the pair generation, into account. In this letter, we study how the generation of position-momentum entangled photon pairs relies on the coherence properties of the pump. For that, we pump a nonlinear crystal by a coherent light sour...

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confidence: 99%

Influence of pump coherence on the generation of position-momentum entanglement in optical parametric down-conversion

Zhang¹,

Fickler²,

Giese³

et al. 2019

Opt. Express

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“…The lengths of the fibers are critical since the walkoff induced to Alice's photons should be the same as Bob's photon. In addition, the walk-off must be less than the pump's coherence time to avoid any distinguishability of the photon pairs, since the coherence time of the entangled photons is transfered from the pump [16,17]. For our experiment the fibers induce a walk-off of approximately 2.34 ps and the coherence time of the 405 ± 0.005 nm pump is approximately 1.08 ns.…”

Section: Methodsmentioning

confidence: 99%

Demonstration of a 6 state-4 state reference frame independent channel for quantum key distribution

Tannous

Jin

et al. 2019

Applied Physics Letters

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We propose and demonstrate a novel protocol for reference frame independent quantum key distribution using six states for Alice and four states for Bob. We show that this protocol can generate a secure key for any possible phase of the entangled state, as long as the variation is small compared to the measurement run, despite the reduced four state measurement in Bob's polarization state analyzer. We perform a proof-of-principle experiment using polarization entangled photon pairs. Despite a rotational phase, we obtain a consistently low error rate of less than 3% indicating the feasibility of this protocol for quantum key distribution. Our protocol is beneficial but not limited to applications in satellite or mobile free-space QKD, where the remote communication node must limit resources and restrict the number of measured states to four instead of six.

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“…Experimentally, it is produced by switching the polarisation of the pump laser between vertical and horizontal polarisations, which is equivalent of using a unpolarised pump. Because entanglement originates fundamentally from a transfer of coherence properties between the pump and the down-converted fields in SPDC [57][58][59], the lack of coherence in the pump polarisation induces the absence of polarisation entanglement in the produced two-photon state, while spatial and temporal entanglement are maintained [22]. See the SI section 5 for further details on state entangled in space but not in polarisation.…”

Section: Phase Distortion Characterisationmentioning

confidence: 99%

“…unpolarised). Due to the fundamental transfer of coherence that occurs between the pump and the down-converted two-photon field in SPDC [57][58][59], the produced state is entangled in space and time, but not in polarisation.…”

Section: Details On Quantum Holography Without Polarisation Entanglementmentioning

confidence: 99%

Polarization entanglement-enabled quantum holography

et al. 2021

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Holography is a cornerstone characterisation and imaging technique that can be applied to the full electromagnetic spectrum, from X-rays to radio waves or even particles such as neutrons. The key property in all these holographic approaches is coherence that is required to extract the phase information through interference with a reference beam -without this, holography is not possible. Here we introduce a holographic imaging approach that operates on intrinsically incoherent and unpolarised beams, so that no phase information can be extracted from a classical interference measurement. Instead, the holographic information is encoded in the second order coherence of entangled states of light. Using spatial-polarisation hyper-entangled photons pairs, we remotely reconstruct phase images of complex objects. Information is encoded into the polarisation degree of the entangled state, allowing us to image through dynamic phase disorder and even in the presence of strong classical noise, with enhanced spatial resolution compared to classical coherent holographic systems. Beyond imaging, quantum holography quantifies hyper-entanglement distributed over 10 4 modes via a spatially-resolved Clauser-Horne-Shimony-Holt inequality measurement, with applications in quantum state characterisation.

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Transfer of temporal coherence in parametric down-conversion

Cited by 16 publications

References 68 publications

Influence of pump coherence on the generation of position-momentum entanglement in optical parametric down-conversion

Influence of pump coherence on the generation of position-momentum entanglement in optical parametric down-conversion

Demonstration of a 6 state-4 state reference frame independent channel for quantum key distribution

Polarization entanglement-enabled quantum holography

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