Quantum Interconnects Achieve >99% Fidelity Wavefunction Transfer Via Phase-Coherent Four-Wave Mixing

The development of robust methods for transferring quantum information between different types of hardware represents a major challenge in building a scalable quantum internet, and now, Hao Zhang, Yang Xu, and Linshan Sun, all from the Department of Electrical and Computer Engineering at UCLA, alongside colleagues including Wei Cui from the University of Ottawa and Robert W. Boyd from the University of Rochester, demonstrate a significant advance in this field. The team achieves high-fidelity phase mapping, exceeding 99%, in transferring quantum states using a process called four-wave mixing, a type of parametric frequency conversion. By systematically investigating spectral phase evolution across a broad range of wavelengths, including infrared to ultraviolet and conversions from telecom to visible and deep-UV light, they reveal that strong phase coherence can be maintained throughout diverse conversion regimes. This preservation of spectral phase is critical for faithful information transfer, and the results establish a promising pathway for integrating different quantum systems and building future communication networks capable of operating across wide spectral domains.

Photon Frequency Conversion and Quantum States

This body of work explores the fundamental principles and technological advancements in quantum optics and information processing, with a strong emphasis on manipulating and converting the quantum states of light. A central theme is frequency conversion, a crucial process for interfacing different quantum systems and enabling communication between them. Researchers are actively developing technologies based on lithium niobate nanophotonic chips and four-wave mixing to achieve efficient frequency conversion and generate entangled photon pairs, a vital resource for quantum communication and computation. Single-photon sources, often utilizing defects in diamond, and their reliable detection are also key areas of investigation, underpinned by the principles of nonlinear optics.

The research extends to the building blocks of quantum computers and networks, investigating various qubit technologies including trapped ions, Rydberg atoms, and defect centers in diamond. Scientists are focused on implementing quantum logic gates for manipulating qubits and building quantum networks, where frequency conversion plays a critical role in connecting different network nodes. Addressing the fragility of quantum states is paramount, leading to investigations into quantum error correction codes and mitigation techniques. A significant portion of the work focuses on miniaturizing quantum optical systems onto chips using nanophotonic chips, microcavities, and metasurfaces, paving the way for practical quantum devices.

Advanced optical techniques, such as dual-comb spectroscopy, are being employed for high-resolution measurements with applications in quantum sensing and metrology. Researchers are also exploring ultraviolet light generation and amplification, and leveraging the low-loss properties of fiber optics for quantum communication. Theoretical studies delve into the fundamental concepts of quantum optics, integrable four-wave mixing Hamiltonians, and the precise description of optical pulses. These investigations collectively aim to advance hybrid quantum systems, scalable quantum networks, integrated quantum photonics, and the development of robust quantum error correction schemes, ultimately pushing the boundaries of quantum technologies.

Broadband Coherent State Transfer in Capillary Fiber

Scientists have developed a novel method for transferring coherent quantum states by utilizing gas-filled hollow-core capillary fiber to investigate how the spectral phase of light evolves across a broad range of wavelengths. This approach allows for the verification of high-fidelity wavefunction phase mapping, exceeding 99%, from input to output fields, demonstrating the potential for efficient information transfer. Researchers successfully achieved conversions from telecom-band wavelengths (1550nm) to visible (516nm) and deep-UV (308nm) wavelengths within the capillary fiber, demonstrating that strong phase coherence can be maintained throughout these diverse conversion regimes, which is crucial for preserving the quantum properties of transmitted information. The experimental setup involves precise tuning of system parameters to achieve efficient and phase-preserving transduction, offering valuable insights into nonlinear coupling dynamics.

Scientists harnessed the unique properties of the hollow-core fiber to facilitate four-wave mixing, a process that enables coherent conversion between photons of vastly different energies. This method overcomes limitations associated with traditional techniques, offering a pathway towards more robust and scalable quantum networks. The team demonstrated conversions bridging a substantial energy difference of approximately 2. 4 eV between ultraviolet and telecom wavelengths, a key challenge in integrating disparate quantum systems. Researchers established that four-wave mixing transduction can achieve conversion efficiencies reaching approximately 33% in certain atomic systems, highlighting the potential for high-performance quantum converters.

The study further demonstrates the ability to maintain strong phase coherence throughout these conversions, essential for preserving quantum attributes like entanglement. By meticulously controlling the experimental conditions within the capillary fiber, scientists achieved a level of fidelity exceeding 99% in the phase mapping of the transferred quantum state, validating the effectiveness of this innovative transduction scheme. This work establishes a promising foundation for advancing four-wave mixing-based transduction schemes and integrating heterogeneous systems across wide spectral domains within future communication networks.

High-Fidelity Quantum State Transfer Across Spectrum

Scientists have demonstrated the feasibility of coherent quantum state transfer by indirectly verifying high-fidelity wavefunction phase mapping, exceeding 99%, from input to output fields. This work utilizes a gas-filled hollow-core capillary fiber to systematically investigate spectral phase evolution across a broad range of wavelengths, encompassing transitions from infrared to ultraviolet light. Experiments reveal that strong phase coherence is maintained throughout these diverse conversion regimes, a critical factor for preserving quantum information. Researchers successfully achieved conversions from telecom-band wavelengths of 1550nm to visible light at 516nm and deep-UV wavelengths of 308nm, consistently maintaining high levels of phase coherence during these transformations.

Further experiments show that efficient and phase-preserving transduction can be achieved by carefully tuning system parameters, providing valuable insights into nonlinear coupling dynamics. These findings establish a strong foundation for advancing four-wave mixing-based quantum transduction schemes and open new avenues for integrating heterogeneous quantum systems across wide spectral domains. The research demonstrates a promising pathway toward building future quantum communication networks capable of linking disparate quantum technologies, such as atomic quantum memories and fiber-based telecom networks, despite significant energy differences, approximately 2. 4 eV, between the wavelengths used for local quantum processing and long-distance transmission. This breakthrough delivers a technically scalable solution for coherent conversion between photons of vastly different energies while preserving essential quantum attributes.

High-Fidelity Phase Conversion Across Spectrum

This research demonstrates high-fidelity phase mapping, exceeding 99%, during coherent state transfer using four-wave mixing in a gas-filled hollow-core capillary fiber. Scientists systematically investigated spectral phase evolution across a broad range of wavelengths, successfully converting signals from the telecom-band (1550nm) to both visible (516nm) and deep-UV (308nm) light. These results confirm that strong phase coherence can be maintained throughout these diverse spectral conversions, which is essential for preserving the information encoded in the amplitude and phase of a photonic wavefunction. The team further showed that efficient and phase-preserving transduction can be achieved by carefully tuning system parameters, providing valuable insights into the dynamics of nonlinear coupling. Investigations into linear, positive quadratic, and negative quadratic phase profiles revealed how different spectral phase structures impact transduction fidelity and quantum coherence, with linear phase modulation demonstrating the preservation of spectral and temporal mode structure. While the experiments were conducted under specific conditions, including a xenon-filled fiber at room temperature, the findings establish a promising pathway for advancing future communication networks by enabling the integration of heterogeneous systems across wide spectral domains.