Cisco is building software to address a fundamental challenge in quantum networking: managing complexity at scale. The company’s Quantum Network Controller is a research prototype designed to deliver Entanglement-as-a-Service (EaaS), allowing applications to request entanglement between quantum processors without direct hardware management, a capability previously not feasible, Cisco says.
Current quantum networks, Cisco notes, are “tightly coupled to specific hardware, configured device by device, with workflows coordinated by hand,” a model the company asserts The Controller aims to overcome these limitations through automatic retry mechanisms and a layered architecture, ultimately striving for fully autonomous operation as networks grow.
Universal Quantum Switch Enables Operable Networks
The prototype addresses a critical gap left by the Universal Quantum Switch, introduced earlier this year, which established the physical connectivity between disparate quantum systems. While connectivity is essential, the Controller provides the intelligence to determine resource allocation, entanglement creation timing and adaptive responses to changing network conditions. A distributed quantum-computing compiler, for example, could request entanglement between processors, with the network autonomously determining the optimal delivery method.
This functionality is enabled by a Hardware Abstraction Layer (HAL) that shields the core architecture from device-specific interfaces. The HAL is foundational to the Controller’s scalability and maintainability, preventing vendor-specific commands from complicating the overall system. The Controller can instruct entanglement sources, configure quantum switches and retrieve time-tag information through a southbound interface, all while remaining agnostic to the specific hardware implementation.
This abstraction allows the protocol engine to operate on quantum operations rather than individual vendor commands. Continuous telemetry data is integral to the Controller’s operation, monitoring source performance, detector state, entanglement success rates and resource use. This data informs routing, scheduling, and resource allocation decisions, while also providing operators with the visibility needed for network optimization and troubleshooting.
The system is designed with automatic retry and reinitialization for failed quantum operations, escalating to human intervention only when necessary. The long-term goal is increasingly autonomous operation as quantum networks scale beyond what people can coordinate by hand. The architecture is designed to handle heterogeneous networks, accommodating diverse quantum processors, memories and switches, each with its own API and capabilities.
The Controller’s design prioritizes abstraction without sacrificing insight into the physical network, recognizing that quantum operations are sensitive to real-time conditions. By decoupling applications from the intricacies of the underlying hardware, Cisco’s prototype seeks to enable scalable, operable quantum networks, moving beyond isolated demonstrations toward practical deployment.
Quantum Network Controller’s Layered Architecture
Cisco’s Quantum Network Controller employs a northbound application programming interface (API) that allows applications to request quantum services without needing to directly manage the underlying hardware, a departure from current systems requiring device-by-device configuration. This API is the entry point for developers seeking to use quantum network capabilities, abstracting away the complexities of the physical layer and enabling a model of Entanglement-as-a-Service (EaaS). The architecture translates these high-level requests into coordinated operations across the network, streamlining the process of accessing and using quantum resources.
A protocol engine within the Controller executes functions like entanglement distribution and swapping, while a scheduler manages resource allocation and timing to optimize network performance. The system is designed to be stateful, event-driven and resource-aware, recognizing the probabilistic and quantum-mechanical nature of quantum networking, a significant difference from classical software-defined networking.
Failure in a quantum network is not always indicative of a problem. Unsuccessful entanglement attempts may simply require retries, resource reconfiguration, or alternative path selection, all handled automatically by the Controller. This automated response aims to reduce manual intervention and increase network resilience, and the foundation for scalability and maintainability lies in the Controller’s Hardware Abstraction Layer (HAL), which isolates higher-level functions from device-specific implementations.
The HAL connects the control plane to entanglement sources, quantum switches, quantum processing unit (QPU) interfaces, detectors, memories, time taggers and synchronization systems, providing a standardized interface for diverse quantum and classical devices. “The goal is not to standardize how quantum devices work internally, but to standardize how each category of device is represented, discovered, monitored, and controlled,” according to the company, enabling heterogeneous hardware to function as a unified, programmable network.
Entanglement-as-a-Service via Northbound API
Applications requesting entanglement between quantum processors will soon bypass direct hardware management, thanks to a layered software architecture developed by Cisco. The Quantum Network Controller, a research prototype, uses a northbound API to translate application requests into coordinated operations across a quantum network, effectively delivering Entanglement-as-a-Service (EaaS).
This approach moves beyond simply connecting quantum devices, addressing the challenge of making a network operable and scalable, a feat previously hindered by manual configuration and device-specific workflows. The Controller’s design acknowledges fundamental differences between classical and quantum networks, particularly the probabilistic nature of entanglement generation and the finite coherence times of qubits.
This is not merely applying software-defined networking to quantum links. It demands a control architecture designed for the inherent quantum-mechanical properties of the network. The company reports that “Applications should be able to request quantum-network services without managing the underlying physics,” envisioning a future where distributed quantum-computing compilers can request entanglement without specifying how it is delivered. A key component enabling this abstraction is the Hardware Abstraction Layer (HAL), which creates a standardized interface between the control software and the physical hardware.
This separation allows for the independent evolution of applications, protocols and hardware, while maintaining a common control model. The system’s protocol engine treats entanglement distribution, swapping and teleportation as native network procedures, executed as stateful, event-driven processes. For example, a quantum teleportation protocol between two processors, QPU-An and QPU-B, requires coordinated resource allocation, entanglement generation and verification before the actual state transfer can begin.
The engine dynamically adjusts to conditions, retrying stages if necessary and preserving successfully established resources. The company states, “Because many quantum operations are probabilistic, the protocol engine also applies predefined retry and reinitialization procedures,” highlighting the system’s resilience and potential for autonomous operation. This architecture ultimately aims to allow applications to consume quantum-network services in a manner analogous to requesting compute or storage in a cloud environment.
Hardware Abstraction Layer Manages Heterogeneous Devices
The Quantum Network Controller employs a Hardware Abstraction Layer (HAL) to manage the inherent diversity of quantum devices, connecting to entanglement sources, quantum switches and quantum processing units through standardized interfaces. This architecture moves beyond direct hardware management, allowing applications to request services like entanglement without needing to understand the specifics of each device’s API, capabilities, or telemetry. The HAL’s function is critical given the practical realities of building quantum networks.
A functioning network will inevitably be heterogeneous, incorporating diverse nodes with differing sources, detectors, memories and processors. If the Controller attempted to directly interpret every device-specific interface, the resulting architecture would quickly become unsustainable; the HAL circumvents this by providing a consistent layer of abstraction. The system’s ability to handle probabilistic operations is also embedded within this layered design. The company notes a long-term commitment to autonomous operation as networks expand.
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