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arXiv:1301.5337 · Physical Review A

Multiphoton quantum interference with high visibility using multiport beam splitters

Magdalena Stobińska, Wiesław Laskowski, Marcin Wieśniak, Marek Żukowski

Published May 23, 2013• 5 citations
arXivHTMLPDF

Abstract

Multiphoton states can be produced in multiple parametric down-conversion (PDC) processes. The nonlinear crystal in such a case is pumped with high power. In theory, the more populated these states are, the deeper is the conflict with local realistic description. However, the interference contrast in multiphoton PDC experiments can be quite low for high pumping. We show how the contrast can be improved. The idea employs currently accessible optical devices, the multiport beam splitters. They are capable of splitting the incoming light in one input mode to $M$ output modes. Our scheme works as a positive operator-valued measure filter. It may provide a feasible Clauser-Horne-Shimony-Holt-Bell inequality test, and thus can be useful in, e.g., schemes reducing communication complexity.

DOI
10.1103/physreva.87.053828

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Multiphoton states can be produced in multiple parametric down-conversion (PDC) processes. The nonlinear crystal in such a case is pumped with high power. In theory, the more populated these states are, the deeper is the conflict with local realistic description. However, the interference contrast in multiphoton PDC experiments can be quite low for high pumping. We show how the contrast can be improved. The idea employs currently accessible optical devices, the multiport beam splitters. They are capable of splitting the incoming light in one input mode to MMM output modes. Our scheme works as a positive operator-valued measure filter. It may provide a feasible Clauser-Horne-Shimony-Holt-Bell inequality test, and thus can be useful in, e.g., schemes reducing communication complexity.
Two spatially separated type-I nonlinear crystals are pumped by femtosecond laser pulses to create entangled photon pairs in the process of spontaneous parametric down-conversion. The two-photon entangled state exhibits high-visibility quantum interference for both polarization and space-time variables without the need of stringent spectral postselection by using narrow-band filters. The visibility is insensitive to the thickness of the crystals, unlike in the case of pulse pumped type-II parametric down-conversion; therefore the intensity can be easily increased by using thick nonlinear crystals. This method will be indispensable in experiments that require a pulsed source of entangled photon pairs, such as generation of multiphoton entangled states, quantum teleportation, and quantum communications.
Double-pair emission from type-II parametric down-conversion results in a highly entangled four-photon state. Due to interference, which is similar to bunching from thermal emission, this state is not simply a product of two pairs. The observation of this state can be achieved by splitting the two emission modes at beam splitters and subsequent detection of a photon in each output. Here we describe the features of this state and construct a Bell-type inequality, which gives a necessary and sufficient condition for a four-photon test of local realistic hidden variable theories.
In photonic quantum technologies, interferometers are one of the key components. They set the stage for essential quantum multiphoton interference, generating and controlling the desired quantum states. Inverse design method revolutionizes such devices by significantly downsizing the interfering region without sacrificing the device performance, offering a viable route to a disruptive photonic architecture of high integration density and low circuit complexity. However, the capability of the inverse-designed interferometers for quantum applications has not yet been fully explored despite the constant development. In this work, we demonstrate multiphoton quantum interference using a topology-optimized tritter with a size of merely 8.0 µm × 4.5 µm. We characterize the tritter and reconstruct its transfer matrix by means of single- and two-photon statistics. We also perform heralded three-photon quantum interference with the tritter. The measured four-fold coincidence features a peak with visibility of (−47.9±8.6)%, which is in fair agreement with the prediction of −55.8% estimated from the reconstructed transfer matrix. Our work confirms successful multiphoton quantum interference at an ultracompact interferometer and demonstrates the possibility of utilizing topology-optimized multiport interferometers for various quantum technologies.
Multiphoton entanglement is an important resource for linear optics quantum computing. Here we show that a wide range of highly entangled multiphoton states, including WWW-states, can be prepared by interfering single photons inside a Bell multiport beam splitter and using postselection. A successful state preparation is indicated by the collection of one photon per output port. An advantage of the Bell multiport beam splitter is that it redirects the photons without changing their inner degrees of freedom. The described setup can therefore be used to generate polarization, time-bin, and frequency multiphoton entanglement, even when using only a single photon source.
Abstract The Hong–Ou–Mandel (HOM) interference is one of the most intriguing quantum optical phenomena and crucial in performing quantum optical communication and computation tasks. Lately, twin beam emitters such as those relying on the process of parametric down-conversion (PDC) have become confident sources of heralded single photons. However, if the pump power is high enough, the pairs produced via PDC—often called signal and idler—incorporate multiphoton contributions that usually distort the investigated quantum features. Here, we derive the temporal characteristics of the HOM interference between heralded states from two independent narrowband PDC sources. Apart from the PDC multiphoton content, our treatment also takes into account effects arriving from an unbalanced beam splitter ratio and optical losses. We perform a simulation in the telecommunication wavelength range and provide a useful tool for finding the optimal choice for PDC process parameters. Our results offer insight in the properties of narrowband PDC sources and turn useful when driving quantum optical applications with them.
Multiphoton interference is crucial to many photonic quantum technologies. In particular, interference forms the basis of optical quantum information processing platforms and can lead to significant computational advantages. It is therefore interesting to study the interference arising from various states of light in large interferometric networks. Here, we implement a quantum walk in a highly stable, low-loss, multiport interferometer with up to 12 ultrafast time bins. This time-bin interferometer comprises a sequence of birefringent crystals that produce pulses separated by 4.3 ps, all along a single optical axis. Ultrafast Kerr gating in an optical fiber is employed to time-demultiplex the output from the quantum walk. We measure one-, two-, and three-photon output states arising from various input state combinations, including a heralded single-photon state, a thermal state, and an attenuated coherent state at one or more input ports. Our results demonstrate that ultrafast time bins are a promising platform to observe large-scale multiphoton interference.