Large-scale integrated sources of quantum light are enabling ingredients for the future of photonic quantum technologies. For such platforms, sources based on electrical injection are of value for their turnkey operation, as they do not rely on bulky off-chip sources to achieve quantum nonlinear conversion. This work presents the first demonstration of a source of entangled photons fully contained in a single waveguide. Our source is based on a single battery-powered Bragg reflection waveguide diode laser producing two indistinguishable sources of ultra-broadband polarization-entangled photons. The output state of our device has a Bell-state fidelity of 86.3% without accidental subtraction, a high entangled pair generation rate of 1.16 × 106 (pairs)/(s ⋅ mW ⋅ facet), and an ultra-broadband entangled photon pair bandwidth >5.22 THz. Our approach yields scalable, compact, low-power, and stable sources of polarization-entangled photons, needed for real-world applications of quantum communications and network systems.
Large-scale integrated sources of quantum light are enabling ingredients for the future of photonic quantum technologies. For such platforms, sources based on electrical injection are of value for their turnkey operation, as they do not rely on bulky off-chip sources to achieve quantum nonlinear conversion. This work presents the first demonstration of a source of entangled photons fully contained in a single waveguide. Our source is based on a single battery-powered Bragg reflection waveguide diode laser producing two indistinguishable sources of ultra-broadband polarization-entangled photons. The output state of our device has a Bell-state fidelity of 86.3% without accidental subtraction, a high entangled pair generation rate of 1.16 × 106 (pairs)/(s ⋅ mW ⋅ facet), and an ultra-broadband entangled photon pair bandwidth >5.22 THz. Our approach yields scalable, compact, low-power, and stable sources of polarization-entangled photons, needed for real-world applications of quantum communications and network systems.
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 explore the potential of versatile and efficient entangled photon pair generation by spontaneous parametric downconversion in Bragg reflection waveguides. By employing a quantum treatment of modes in channel waveguides, and by accounting for group velocity dispersion in the modes, the quantum state of the generated biphotons is realistically calculated. The pair production rate is predicted to reach 4×108 pairs/s/nm/mW of pump light in a 2 mm-long structure, on par with or exceeding the performance of previously reported designs. This is attributable to an enhanced nonlinear interaction through tight mode confinement in the waveguide. Strategies for device performance optimization and phase matching wavelength tunability are outlined and numerically demonstrated. The proposed design platform is versatile and allows photon pair generation with controllable flux, bandwidth, Schmidt number, and degree of polarization entanglement. The possibility of monolithic integration with a diode laser pump offers a way to design an electrically pumped entangled photon source.
Entangled photons are fundamental resources for quantum communication, computing, and networking. Among them, polarization-entangled photon pairs play an important role due to their straightforward state manipulation and direct use in quantum key distribution, teleportation, and network protocols. However, realizing compact, efficient, and scalable polarization-entangled sources that meet the requirements of practical deployment remains a major challenge. Here, we present a simple yet high-performance on-chip polarization-entangled photon-pair source on thin-film lithium niobate (TFLN). Our device employs dual quasi-phase matching (D-QPM) that sequentially supports type-0 and type-I spontaneous parametric down-conversion in a single nanophotonic waveguide, eliminating the need for interferometers, polarization rotators, or other complex circuits. The source directly produces high-fidelity Bell states with broad bandwidth, high brightness, and low noise. Using this integrated platform, we realize wavelength-multiplexed entanglement distribution in a four-user quantum network deployed over metropolitan fiber links up to 50 km. These results establish a robust and scalable pathway toward practical quantum communication systems and multi-user quantum mesh networks based on integrated photonics.
Integrated quantum photonics furthers several quantum information protocols; one key feature of the on-chip setting is its potential for massively scalable quantum systems while operating with stability unseen in free-space optics. In this thesis, I develop theories, techniques, and sources to aid in developing potential future large-scale integrated quantum systems. A photon subtraction-based entanglement enhancement protocol for continuous-variable quantum networks is presented. The scheme shows that states generated with multiple single-mode squeezed input states, rather than a single input source, can be more sensitive to entanglement enhancement. To work toward implementing networks of squeezed light sources, an injection-locked pump laser for a spontaneous parametric downconversion (SPDC) process using a weak second harmonic generation signal is shown to be more power efficient compared to other conventional approaches. This injection-locking paradigm illustrates a novel approach to stabilize the phase of the pump of future integrated systems. Ideal quantum information platforms will achieve the integration of every element, including the pump. This thesis demonstrated the first battery-powered polarization-entangled photon source which was achieved using Bragg reflection waveguide laser diodes (BRLs). The output state with (without) accidentals subtracted from this device has a Bell-state fidelity of 98.0% (86.3%), a high brightness of 1.04*10^6 (pairs)/(s mW facet), and ultra-broadband entangled photon pairs, > 5.22 THz. I also adapted the BRLs to convert polarization-entanglement to time-energy entanglement with a visibility of 91%. Additionally, hyperentangled polarization and time-energy states with visibilities of 95.5% and 86% were demonstrated for the respective degrees of freedom after the subtraction of accidentals. The approach presented yields scalable, compact, low-power, stable, and room-temperature operated sources of polarization-entangled photons needed for quantum communications and network systems. Identical photon pairs allow for quantum interference of the photon states of interest. One important demonstration is the time-reversed Hong-Ou-Mandel (TRHOM) effect, which can achieve the deterministic separation of photon pairs. The BRLs presented in this work produce two outputs; hence, I demonstrate BRL with a TRHOM interference visibility of 89%. This TRHOM demonstration shows that BRLs are ideal candidates for current discrete variables and show future potential for continuous variable quantum information protocols.
Abstract Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust, and scalable chip formats with applications in long-distance quantum-secured communication, quantum-accelerated information processing, and non-classical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers making them impractical, not reproducible prototype devices, hindering scalability and the transfer out of the lab into real-world applications. Here we demonstrate a fully integrated quantum light source, which overcomes these challenges through the combined integration of a laser cavity, a highly efficient tunable noise suppression filter (> 55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically-pumped InP gain section and a Si₃N₄ low-loss microring filter system and demonstrates high-performance parameters, i.e., a pair emission over four resonant modes in the telecom band (bandwidth ∼ 1 THz), and a remarkable pair detection rate of ∼ 620 Hz at a high coincidence-to-accidental ratio of ∼80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), verified by quantum interference measurements with visibilities up to 96% (violating Bell-inequality) and by density matrix reconstruction through state tomography showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables commercial-viable, low-cost, compact, light-weight, and field-deployable entangled quantum sources, quintessential for practical, out-of-lab applications, e.g., in quantum processors and quantum satellite communications systems.
Abstract Integrated optics provides the platform for the experimental implementation of highly complex and compact circuits for quantum information applications. In this context integrated waveguide sources represent a powerful resource for the generation of quantum states of light due to their high brightness and stability. However, the confinement of the light in a single spatial mode limits the realization of multi-channel sources. Due to this challenge one of the most adopted sources in quantum information processes, i.e. a source which generates spectrally indistinguishable polarization entangled photons in two different spatial modes, has not yet been realized in a fully integrated platform. Here we overcome this limitation by suitably engineering two periodically poled waveguides and an integrated polarization splitter in lithium niobate. This source produces polarization entangled states with fidelity of F=0.973±0.003 F = 0.973 ± 0.003 and a test of Bell’s inequality results in a violation larger than 14 standard deviations. It can work both in pulsed and continuous wave regime. This device represents a new step toward the implementation of fully integrated circuits for quantum information applications.