Photon temporal modes: a complete framework for quantum information science (1504.06251v4)

Abstract: Field-orthogonal temporal modes of photonic quantum states provide a new framework for quantum information science (QIS). They intrinsically span a high-dimensional Hilbert space and lend themselves to integration into existing single-mode fiber communication networks. We show that the three main requirements to construct a valid framework for QIS -- the controlled generation of resource states, the targeted and highly efficient manipulation of temporal modes and their efficient detection -- can be fulfilled with current technology. We suggest implementations of diverse QIS applications based on this complete set of building blocks.

• The paper introduces photon temporal modes as a high-dimensional resource for quantum state encoding.
• The paper demonstrates controlled generation and manipulation of temporal modes via engineered dispersion and quantum pulse gates.
• The paper highlights applications in multiplexing, secure quantum key distribution, and computation within integrated fiber networks.

Photon Temporal Modes: A Comprehensive Framework for Quantum Information Science

The paper "Photon temporal modes: a complete framework for quantum information science," by Brecht et al., presents an innovative framework for quantum information science (QIS) based on the utilization of photon temporal modes (TMs). TMs offer a high-dimensional Hilbert space, suitable for efficient integration into current single-mode fiber communication infrastructure. The authors assert that the main prerequisites for a credible QIS framework—controlled generation of resource states, efficient manipulation, and reliable detection of temporal modes—are achievable with existing technologies.

Core Concepts and Definitions

The paper introduces TMs as a novel basis for photonic quantum states, highlighting that they can be used effectively for information encoding. TMs are broadband, field-orthogonal wave-packet states that can span infinite dimensional Hilbert spaces, unlike polarization modes which are limited to two dimensions. The Hilbert space spanned by TMs offers potential improvements in both the information capacity per photon and the security of quantum communication systems.

The authors postulate that a substantial advantage of TMs lies in their compatibility with current single-mode fiber networks, which makes TMs robust against common medium perturbations such as linear dispersion. This attribute enhances their viability for practical quantum communication as well as implementation in hybrid quantum networks requiring interfacing between photons and matter-based qubits.

State-of-the-Art and Photon Pair Generation

The current state-of-the-art in TM generation primarily involves parametric down-conversion (PDC) processes. The structure of photon pairs generated via PDC is characterized by a Joint Spectral Amplitude (JSA), which reveals the underlying TM structure of the entangled photon pairs. The typical challenge with current PDC methods is the limited control over the dimensions of the TM space, which is critical for encoding complex quantum information. The authors propose solutions involving engineered dispersion in nonlinear optical waveguides, enabling precise control over TM pair generation, potentially leading to TM Bell states.

Photon TM State Control and Quantum Pulse Gates (QPGs)

The authors introduce QPGs as crucial devices for manipulating TMs. QPGs function by selectively converting specific TMs into another frequency band, allowing for the coherent manipulation of quantum states. The paper indicates that two-stage QPG configurations can achieve high selectivity and conversion efficiencies, crucial for reliable TM manipulation. The fidelity and selectivity of these operations are pivotal for quantum computation and communication applications as they influence the success rate of TM filtering and relocation processes.

Quantum Information Science (QIS) Applications

This TM framework has various applications within QIS, as follows:

1. TM Multiplexing for Quantum Communication: The paper outlines a TM multiplexing strategy where different TMs are used as independent communication channels, facilitating higher density information transmission through single-mode fibers with minimal cross-talk.
2. High-Dimensional Quantum Key Distribution (QKD): By exploiting the high-dimensional space accessible through TMs, enhanced QKD schemes can be realized. This promises an increased security threshold against eavesdropping attacks.
3. Quantum Computation with TMs: The combination of QPGs and TMs supports single- and multi-qubit operations, forming the foundation for linear optical quantum computation (LOQC). The framework also allows for the preparation and manipulation of cluster states, a requisite for cluster-state quantum computation.

Challenges and Future Developments

While the TM framework offers significant potential for QIS applications, several challenges remain. Key among these are the efficient implementation of QPGs with high selectivity and the precise generation of entangled TM states. The current technological constraints on the spectral bandwidth and resolution of pulse shapers also limit the achievable dimensionality of the TM space. Nonetheless, advancements in integrated photonic device fabrication and timing electronics are expected to mitigate these challenges over time.

In conclusion, the authors propose a comprehensive framework based on TMs that promise enhanced compatibility with existing networks and robustness against perturbations. Continual advancements in QPG technology and pulse shaping are essential to unlocking the full potential of this approach, thus enabling advanced QIS applications such as high-dimensional qudit systems and secure quantum communication networks. This work suggests a transformative direction in QIS, exploiting the temporal degree of freedom to achieve scalable and efficient quantum networks.