Frequency-encoded photonic qubits for scalable quantum information processing (1612.03131v1)

Abstract: Among the objectives toward large-scale quantum computation is the quantum interconnect: a device which uses photons to interface qubits that otherwise could not interact. However, current approaches require photons indistinguishable in frequency---a major challenge for systems experiencing different local environments or of different physical compositions altogether. Here we develop an entirely new platform which actually exploits such frequency mismatch for processing quantum information. Labeled "spectral linear optical quantum computation" (spectral LOQC), our protocol offers favorable linear scaling of optical resources and enjoys an unprecedented degree of parallelism, as an arbitrary $N$-qubit quantum gate may be performed in parallel on multiple $N$-qubit sets in the same linear optical device. Not only does spectral LOQC offer new potential for optical interconnects; it also brings the ubiquitous technology of high-speed fiber optics to bear on photonic quantum information, making wavelength-configurable and robust optical quantum systems within reach.

• The paper proposes a spectral LOQC framework using distinct frequency modes to encode quantum information, enabling efficient photon-based processing.
• It demonstrates linear scaling and parallel operations by leveraging standard telecom components like Fourier-transform pulse shapers and electro-optic modulators.
• The study outlines a universal gate set and practical strategies for implementing scalable photonic quantum computing architectures.

Frequency-Encoded Photonic Qubits for Scalable Quantum Information Processing

The paper "Frequency-encoded photonic qubits for scalable quantum information processing" by Joseph M. Lukens and Pavel Lougovski introduces a paradigm shift in the field of quantum information processing using photons. The authors propose a novel framework termed "spectral linear optical quantum computation" (spectral LOQC) that leverages the frequency of photonic modes to encode quantum information, rather than relying on spatial or polarization modes traditionally used in quantum optical architectures.

Key Insights and Contributions

1. Spectral Encoding: The core innovation of spectral LOQC is the utilization of distinct frequency modes for encoding qubits. This approach addresses significant challenges associated with ensuring identical frequency for photon interaction in heterogeneous systems, thereby facilitating quantum processing in systems with mismatched frequencies.
2. Linear Scaling and Parallelism: The protocol promises favorable linear scaling of optical resources. Notably, it permits carrying out quantum operations in parallel across multiple qubits within the same device, resulting in an efficient utilization of quantum resources.
3. Component Utilization: The protocol relies on well-established optical telecommunication components such as Fourier-transform pulse shapers and electro-optic modulators (EOMs) to manipulate photonic qubits. These devices, prevalent in classical high-speed fiber optics, offer flexibility through electrical control and compatibility with dense wavelength-division multiplexing (DWDM), streamlining integration with existing technology.
4. Universal Gate Set: The paper derives a universal set of quantum operations within this framework—single-qubit phase and Hadamard gates, and a controlled-Z (cz) gate for two-qubit operations. The authors provide a detailed protocol with a linear scaling behavior for the computational resources, achieving success probabilities in line with currently known theoretical maxima in purely linear optical settings.
5. Practicality and Implementation: The approach is well-aligned with contemporary technological capabilities. With realistic estimates of spectral resolution and modulation bandwidth in current telecommunications technology, the feasibility of spectral LOQC is underscored. The paper outlines a potential setup for experimental realization, pointing towards a fully integrated approach in the future.

Implications and Future Work

The spectral LOQC framework posits significant implications for quantum information science, particularly in the construction of quantum interconnects that enable disparate systems to communicate efficiently. The method's intimacy with DWDM technology suggests a viable path toward scalability and integration with existing classical optical networks, potentially influencing the development of the quantum internet.

Future developments could involve refining the components to minimize losses, optimizing the configuration for parallel operation of multiple qubits, and exploring practical chip-scale implementations for greater integration. Addressing the scalability of these systems and investigating the coherence preservation over extended networks will be crucial for realizing the vision of robust quantum communication channels.

Moreover, moving beyond the demonstration stage to active error correction and fidelity improvements stands as a focal point for subsequent research endeavors. As the field progresses, the role of spectral LOQC in hybrid quantum-classical systems may expand, fostering new avenues for collaboration between quantum and opto-electronic technologies.

In conclusion, the paper lays a foundational framework for future exploration and provides a blueprint towards overcoming some of the primary hurdles in photonic quantum computing, thus contributing substantially to the roadmap for practical quantum computing architectures.