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arXiv:1511.01963 · Physical Review A

Two polarization-entangled sources from the same semiconductor chip

Dongpeng Kang, Minseok Kim, Haoyu He, Amr Saher Helmy

Published Jul 13, 2015• 16 citations
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Abstract

Generating nonclassical states of photons such as polarization-entangled states on a monolithic chip is a crucial step towards practical applications of optical quantum information processing such as quantum computing and quantum key distribution. Here we demonstrate two polarization-entangled photon sources in a single monolithic semiconductor waveguide. The first source is achieved through the concurrent utilization of two spontaneous parametric down-conversion (SPDC) processes, namely, type-0 and type-I SPDC processes. The chip can also generate polarization-entangled photons via the type-II SPDC process, enabling the generation of both copolarized- and cross-polarized polarization-entangled photons in the same device. In both cases, polarization entanglement is generated directly on the chip without the use of any off-chip compensation, interferometry, or bandpass filtering. This enables direct, chip-based generation of both Bell states $(|H,H\ensuremath{\rangle}+|V,V\ensuremath{\rangle})/\sqrt{2}$ and $(|H,V\ensuremath{\rangle}+|V,H\ensuremath{\rangle})/\sqrt{2}$ simultaneously utilizing the same pump source. In addition, based on compound semiconductors, this chip can be directly integrated with it own pump laser. This technique ushers an era of self-contained, integrated, electrically pumped, room-temperature polarization-entangled photon sources.

DOI
10.1103/physreva.92.013821

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Generating nonclassical states of photons such as polarization-entangled states on a monolithic chip is a crucial step towards practical applications of optical quantum information processing such as quantum computing and quantum key distribution. Here we demonstrate two polarization-entangled photon sources in a single monolithic semiconductor waveguide. The first source is achieved through the concurrent utilization of two spontaneous parametric down-conversion (SPDC) processes, namely, type-0 and type-I SPDC processes. The chip can also generate polarization-entangled photons via the type-II SPDC process, enabling the generation of both copolarized- and cross-polarized polarization-entangled photons in the same device. In both cases, polarization entanglement is generated directly on the chip without the use of any off-chip compensation, interferometry, or bandpass filtering. This enables direct, chip-based generation of both Bell states (∣H,H\ensuremath⟩+∣V,V\ensuremath⟩)/2(|H,H\ensuremath{\rangle}+|V,V\ensuremath{\rangle})/\sqrt{2}(∣H,H\ensuremath⟩+∣V,V\ensuremath⟩)/2​ and (∣H,V\ensuremath⟩+∣V,H\ensuremath⟩)/2(|H,V\ensuremath{\rangle}+|V,H\ensuremath{\rangle})/\sqrt{2}(∣H,V\ensuremath⟩+∣V,H\ensuremath⟩)/2​ simultaneously utilizing the same pump source. In addition, based on compound semiconductors, this chip can be directly integrated with it own pump laser. This technique ushers an era of self-contained, integrated, electrically pumped, room-temperature polarization-entangled photon sources.
Quantum states of photons such as entangled and single photons are indispensable components for applications in optical quantum information processing. Being able to generate and manipulate quantum states of photons on a chip is a crucial step towards realizing real-world quantum information processing systems such as an optical quantum computer. In this thesis, theoretical and experimental research was carried out for on-chip generation of quantum states of photons via the nonlinear process of spontaneous parametric down-conversion (SPDC), including polarization entangled photons, hyperentangled photons and heralded pure single photons. A majority of the study was based on III-V semiconductor AlGaAs, which could lead to monolithic integration of pump lasers and enable electrically pump sources operating at room temperature. The generation of cross-polarized entangled photons via a type-II SPDC in an AlGaAs Bragg reflection waveguide (BRW) was first investigated. The lack of material birefringence enables the direct generation of wavelength-multiplexed polarization entangled photons with a concurrence of at least 0.77 in a bandwidth of 95 nm. Second, a technique using concurrent type-0 and type-I processes on an AlGaAs chip to generate polarization entangled photon was developed. This technique allows the generation of both co-polarized and cross-polarized entangled photons on the same chip without the need of off-chip compensation, interferometer and bandpass filter. Third, a technique of generating hyperentangled photons on an AlGaAs chip was developed by utilizing spatial modes of different guiding mechanisms. High quality entanglement could be achieved with bandpass filtering of a few nanometers without off-chip phase compensation. Four, a generic technique using nonlinear photonic nanowires to engineer two-photon quantum states was proposed. Via dispersion engineering which controls the group velocity of each mode, maximally entangled polarization entangled photons and pure heralded single photons can be generated on-chip. Design examples were applied to III-V semiconductor and ferroelectric materials. Last, a strategy to enhance the bandwidths of wavelength conversion and SPDC spectrum was developed by tapering the waveguides. Combined with further integration of pump lasers, photonic circuits and detectors, the techniques developed in this thesis provides a viable route to achieve fully integrated generation and manipulations of photonic quantum qubits.
Generating entangled photons on monolithic chips is a significant progress towards real-life applications of optical quantum information processing such as quantum key distribution and quantum computing. Here we present our recent achievements in generating polarization entangled photons on monolithic III-V semiconductor chips without any off-chip component. We demonstrate the direct generation of broadband polarization entangled photons from a semiconductor chip for the first time with a record degree of entanglement. We also show an alternative approach for polarization entangled photon generation on the same epitaxial structure, which enabled a single chip generating both co-polarized and cross-polarized entangled photons. With recent progress on pump laser integration, our results pave the way for fully integrated entangled photon sources in the foreseeable future.
We propose and analyze the performance of a technique to generate mode and polarization hyperentangled photons in monolithic semiconductor waveguides using two concurrent type-II spontaneous parametric downconversion (SPDC) processes.These two SPDC processes are achieved by waveguide engineering which allows for simultaneous modal phase matching with the pump beam in a higher-order mode.Paired photons generated in each process are cross polarized and guided by different guiding mechanisms, which produces entanglement in both polarization and spatial mode.Theoretical analysis shows that the output quantum state has a high quality of hyperentanglement by spectral filtering with a bandwidth of a few nanometers, while off-chip compensation is not needed.This technique offers a path to realize an electrically pumped hyperentangled photon source.
Generating entangled photons from a monolithic chip is a major milestone towards real-life applications of optical quantum information processing including quantum key distribution and quantum computing. Ultrabroadband entangled photons are of particular interest to various applications such as quantum metrology and multi-party entanglement distribution. In this work, we demonstrate the direct generation of broadband wavelength-multiplexed polarization entangled photons from a semiconductor chip for the first time. Without the use of any off-chip compensation or interferometry, entangled photons with a signal-idler separation as large as 95 nm in the telecom band were observed. The highest concurrence of 0.98±0.01 achieved in this work is also the highest, to the best of our knowledge, comparing to all previously demonstrated semiconductor waveguide sources. This work paves the way for fully integrated, ultrabroadband sources of polarization entangled photons.
We demonstrate the first all-on-chip source of entangled photons in polarization or time-energy. Our source is a monolithic Bragg reflection laser diode with intracavity phase matching, enabling a type-II spontaneous parametric down-conversion process. This plug-and-play, electrically injected chip source operates at room temperature and does not require active stabilization. The entangled biphoton state emitted from the chip is in the telecom band, with a bandwidth of 5.56 THz, achieving a pair rate of 5.6 × 105pairs/s. Additionally, a visibility of 76.2% and 58% was obtained for the polarization and time-energy entanglements, respectively. Hence, our source opens the possibility for massively parallel systems from a compact and low-power chip.
We demonstrate the direct generation of polarization-entangled photon pairs at room temperature and telecom wavelength in an AlGaAs semiconductor waveguide. The source is based on spontaneous parametric down-conversion with a counterpropagating phase-matching scheme. The quality of the two-photon state is assessed by the reconstruction of the density matrix giving a raw fidelity to a Bell state of 0.83; a theoretical model, taking into account the experimental parameters, provides ways to understand and control the amount of entanglement. Its compatibility with electrical injection, together with the high versatility of the generated two-photon state, make this source an attractive candidate for completely integrated quantum photonics devices.