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Versatile Quantum State Generation and Manipulation in a Programmable Silicon-Photonic 4-Qubit System with High-Fidelity and Purity

Jong-Moo Lee, Jeongho Bang, Jiho Park, Young-Ik Sohn, Alessio Baldazzi, Matteo Sanna, Stefano Azzini, Lorenzo Pavesi

Published Dec 26, 2023• 0 citations
Publisher

Abstract

We present a programmable Silicon Photonic 4-qubit integrated circuit for the generation and manipulation of diverse quantum states. The Silicon Photonic chip integrates photon-pair sources, pump-removing filters, wavelength-division-multiplexing (WDM) filters, Mach-Zehnder Interferometer (MZI) switches, and single-qubit arbitrary gates, enabling versatile state preparation and tomography. We measure Hong-Ou-Mandel (HOM) interference with an impressive 98% visibility using 4-photon coincidence, laying the foundation for high-purity qubits. Our analysis involves estimating the fidelity and purity of distinct quantum states through maximum-likelihood estimation (MLE) applied to tomographic measurements. In our experimental results, we showcase the following achievements: a heralded single qubit achieving 98.2% fidelity and 98.3% purity, a Bell state reaching 95.2% fidelity and 94.8% purity, and a 4-qubit system with two simultaneous Bell states exhibiting 87.4% fidelity and 84.6% purity. Finally, a 4-qubit Greenberger–Horne–Zeilinger (GHZ) state demonstrates 85.4 % fidelity and 81.7% purity. Additionally, we certify the entanglement of the 4-photon GHZ state through Bell's inequality violations and a negative entanglement witness.

DOI
10.1364/opticaopen.24901572

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We present a programmable Silicon Photonic 4-qubit integrated circuit for the generation and manipulation of diverse quantum states. The Silicon Photonic chip integrates photon-pair sources, pump-removing filters, wavelength-division-multiplexing (WDM) filters, Mach-Zehnder Interferometer (MZI) switches, and single-qubit arbitrary gates, enabling versatile state preparation and tomography. We measure Hong-Ou-Mandel (HOM) interference with an impressive 98% visibility using 4-photon coincidence, laying the foundation for high-purity qubits. Our analysis involves estimating the fidelity and purity of distinct quantum states through maximum-likelihood estimation (MLE) applied to tomographic measurements. In our experimental results, we showcase the following achievements: a heralded single qubit achieving 98.2% fidelity and 98.3% purity, a Bell state reaching 95.2% fidelity and 94.8% purity, and a 4-qubit system with two simultaneous Bell states exhibiting 87.4% fidelity and 84.6% purity. Finally, a 4-qubit Greenberger–Horne–Zeilinger (GHZ) state demonstrates 85.4 % fidelity and 81.7% purity. Additionally, we certify the entanglement of the 4-photon GHZ state through Bell's inequality violations and a negative entanglement witness.
We present a programmable Silicon Photonic 4-qubit integrated circuit for the generation and manipulation of diverse quantum states. The Silicon Photonic chip integrates photon-pair sources, pump-removing filters, wavelength-division-multiplexing (WDM) filters, Mach-Zehnder Interferometer (MZI) switches, and single-qubit arbitrary gates, enabling versatile state preparation and tomography. We measure Hong-Ou-Mandel (HOM) interference with an impressive 98% visibility using 4-photon coincidence, laying the foundation for high-purity qubits. Our analysis involves estimating the fidelity and purity of distinct quantum states through maximum-likelihood estimation (MLE) applied to tomographic measurements. In our experimental results, we showcase the following achievements: a heralded single qubit achieving 98.2% fidelity and 98.3% purity, a Bell state reaching 95.2% fidelity and 94.8% purity, and a 4-qubit system with two simultaneous Bell states exhibiting 87.4% fidelity and 84.6% purity. Finally, a 4-qubit Greenberger–Horne–Zeilinger (GHZ) state demonstrates 85.4 % fidelity and 81.7% purity. Additionally, we certify the entanglement of the 4-photon GHZ state through Bell's inequality violations and a negative entanglement witness.
We present a programmable silicon photonic four-qubit integrated circuit for the generation and manipulation of diverse quantum states. The silicon photonic chip integrates photon-pair sources, pump-reducing filters, wavelength-division-multiplexing filters, Mach–Zehnder interferometer switches, and single-qubit arbitrary gates, enabling versatile state preparation and tomography. We measure Hong–Ou–Mandel interference with an impressive 98% visibility using four-photon coincidence, laying the foundation for high-purity qubits. Our analysis involves estimating the fidelity and purity of distinct quantum states through maximum-likelihood estimation applied to tomographic measurements. In our experimental results, we showcase the following achievements: a heralded single qubit achieving 98.2% fidelity and 98.3% purity, a Bell state reaching 95.2% fidelity and 94.8% purity, and a four-qubit system with two simultaneous Bell states exhibiting 87.4% fidelity and 84.6% purity. Finally, a four-qubit Greenberger–Horne–Zeilinger (GHZ) state demonstrates 85.4% fidelity and 81.7% purity. In addition, we certify the entanglement of the four-photon GHZ state through Bell’s inequality violations and a negative entanglement witness.
Photonic integrated circuits offer a scalable and robust route toward quantum information technologies by consolidating photon sources and linear optical networks onto compact, wafer-manufacturable chips. Although silicon photonics has enabled diverse discrete-variable quantum breakthroughs -- spanning multiphoton entanglement, quantum networking, and photonic qubit fusion for quantum computing -- scaling these platforms beyond proof-of-principle demonstrations remains severely constrained by a critical system-level bottleneck. Optical loss compounds rapidly across photon generation, routing, and state analysis, causing multiphoton generation probabilities to plummet exponentially as circuit depth and complexity grow. Here we overcome this rate-loss barrier by demonstrating a monolithic, ultralow-loss silicon nitride (Si3_33​N4_44​) integrated photonic platform engineered for high-performance discrete-variable quantum information processing. Our architecture seamlessly integrates narrowband photon-pair sources with low-loss qubit-fusion circuits and reconfigurable state-analysis interferometers. The on-chip sources prepare Einstein-Podolsky-Rosen (EPR) states with a fidelity of 0.9875(3) and exhibit near-unity photon indistinguishability, yielding a heralded Hong-Ou-Mandel interference visibility of 0.990(6). By executing on-chip fusion of two EPR states, we synthesize and characterize four-photon Greenberger-Horne-Zeilinger states with a record fidelity of 0.943(8) and a fourfold count rate of 27 Hz -- more than two orders of magnitude higher than previous silicon-photonic implementations. Combined with standard CMOS-compatible fabrication on 150-mm-diameter wafers, these results establish ultralow-loss Si3_33​N4_44​ integrated photonics as a definitive, manufacturable platform for deployable, large-scale quantum information processors.
Mutually entangled multi-photon states are at the heart of all-optical quantum technologies. While impressive progresses have been reported in the generation of such quantum light states using free space apparatus, high-fidelity high-rate on-chip entanglement generation is crucial for future scalability. In this work, we use a bright quantum-dot based single-photon source to demonstrate the high fidelity generation of 4-photon Greenberg-Horne-Zeilinger (GHZ) states with a low-loss reconfigurable glass photonic circuit. We reconstruct the density matrix of the generated states using full quantum-state tomography reaching an experimental fidelity to the target ∣GHZ4⟩|{\text{GHZ}_4}\rangle∣GHZ4​⟩ of FGHZ4(86.0±0.4) %\mathcal{F}_{\text{GHZ}_4} (86.0\pm0.4)\,\%FGHZ4​​(86.0±0.4)%, and a purity of PGHZ4=(76.3±0.6) %\mathcal{P}_{\text{GHZ}_4}=(76.3\pm0.6)\,\%PGHZ4​​=(76.3±0.6)%. The entanglement of the generated states is certified with a semi device-independent approach through the violation of a Bell-like inequality by more than 39 standard deviations. Finally, we carry out a four-partite quantum secret sharing protocol on-chip where a regulator shares with three interlocutors a sifted key with up to 1978 bits, achieving a qubit-error rate of 10.87 %10.87\,\%10.87%. These results establish that the quantum-dot technology combined with glass photonic circuitry for entanglement generation on chip offers a viable path for intermediate scale quantum computation and communication.
Abstract Mutually entangled multi-photon states are at the heart of all-optical quantum technologies. While impressive progresses have been reported in the generation of such quantum light states using free space apparatus, high-fidelity high-rate on-chip entanglement generation is crucial for future scalability. In this work, we use a bright quantum-dot based single-photon source to demonstrate the high fidelity generation of 4-photon Greenberg-Horne-Zeilinger (GHZ) states with a low-loss reconfigurable glass photonic circuit. We reconstruct the density matrix of the generated states using full quantum-state tomography reaching an experimental fidelity to the target state of FGHZ4=(86.0±0.4) %{{{{\mathcal{F}}}}}_{{{{{\rm{GHZ}}}}}_{4}}=(86.0\pm 0.4)\, \%FGHZ4​​=(86.0±0.4)% F GHZ 4 = ( 86.0 ± 0.4 ) % , and a purity of PGHZ4=(76.3±0.6) %{{{{\mathcal{P}}}}}_{{{{{\rm{GHZ}}}}}_{4}}=(76.3\pm 0.6)\, \%PGHZ4​​=(76.3±0.6)% P GHZ 4 = ( 76.3 ± 0.6 ) % . The entanglement of the generated states is certified with a semi device-independent approach through the violation of a Bell-like inequality by more than 39 standard deviations. Finally, we carry out a four-partite quantum secret sharing protocol on-chip where a regulator shares with three interlocutors a sifted key with up to 1978 bits, achieving a qubit-error rate of 10.87%. These results establish that the quantum-dot technology combined with glass photonic circuitry offers a viable path for entanglement generation and distribution.