Fully on-chip photonic turnkey quantum source for entangled qubit/qudit state generation

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.

Quantum and coherent signal transmission on a single-frequency channel via the electro-optic serrodyne technique

“…The RF waveforms were generated by an AWG (Keysight M8194A, up to 45-GHz analog bandwidth) and subsequently amplified by broadband power amplifiers (RF Lambda up to 35-GHz bandwidth, RF Lambda up to 28-GHz bandwidth). For the combined transmission of quantum and coherent signals via the serrodyne transceiver, we applied the optimized RF waveform cos(ft + α) cos(πt/2) 16 with a carrier frequency of f/(2π) = 20 GHz to the electro-optic phase modulators, where α is the carrier-envelope offset phase. The envelope was chosen such that it falls off fast in frequency domain and hence is compatible with the limited gain bandwidth (~10 to 28 GHz) of the RF amplifiers used.…”

Parallelization of frequency domain quantum gates: manipulation and distribution of frequency-entangled photon pairs generated by a 21 GHz silicon microresonator

“…This scheme has gained interest since 2017, when a universal scheme for quantum information with frequency-encoding was proposed 1 . Frequency-encoded entangled states are a major resource for quantum information and have since been generated in various nanophotonics structures, such as the Hydex microresonator (MR) (2017), 2 silicon nitride MRs (2018–2023), 3 – 5 lithium niobate waveguides, 4 , 6 – 8 and while frequency-entanglement can occur in any silicon-on-insulator (SOI) resonator generating photon pairs, it has only recently been observed on the SOI platform, combining SOI MRs 9 – 11 The frequency bins are created by external filtering of the wideband nonlinear sources, 6 – 8 , 12 or by exploiting the inherently discrete frequencies of the resonators 2 , 4 , 9 , 10 …”

>20 dB phase noise reduction by locking an off-the-shelf external cavity laser having sub-kHz linewidth to an on-chip wavelength reference in Si3N4 using an electronic feedback loop on the diode injection current

“…The used aMZI structure is made onto a separate photonic integrated chip (PIC), making the presented results form the basis of the first stepping stone towards PIC based lasers having an on-chip wavelength reference inside a super compact and robust formfactor. Such stabilized, wavelength agile lasers find their way into many applications in the field of quantum applications, optical clocks, telecommunication and many more [1][2][3]. The wavelength of the presented laser can be freely tuned across the c-telecom bandwidth, and similar designs prove to scan at much broader wavelength ranges, yet providing tens of mW of output power [4,5].…”