Toshiba develops QKD on a chip

Applications and Research

Toshiba Europe Ltd has developed the world’s first chip-based quantum key distribution (QKD) system. The company says this advance will enable the mass manufacture of quantum security technology, bringing its application to a much wider range of scenarios including to Internet of Things (IoT) solutions.

Toshiba has developed techniques for shrinking the optical circuits used for QKD and QRNG into tiny semiconductor chips. These are not only much smaller and lighter than their fibre optic counterparts, but also consume less power. Most significantly, many can be fabricated in parallel on the same semiconductor wafer using standard techniques used within the semiconductor industry, allowing them to be manufactured in much larger numbers. For example, the quantum transmitter chips developed by Toshiba measure just 2x6mm, allowing several hundred chips to be produced simultaneously on a wafer.

Toshiba says that to promote integration into conventional communication infrastructures, the QKD units are assembled in compact 1U rackmount cases. The QRx and QTx chips are packaged into C-form-factor-pluggable-2 (CFP2) modules, a widespread form-factor in coherent optical communications, to ensure forward compatibility of the system with successive QKD chip generations, making it easily upgradeable. Off-the-shelf 10 Gb/s small-form-factor pluggable (SFP) modules are used for the public communication channels.

Andrew Shields, head of Quantum Technology at Toshiba Europe, remarked, “Photonic integration will allow us to manufacture quantum security devices in volume in a highly repeatable fashion. It will enable the production of quantum products in a smaller form factor, and subsequently allow the roll out of QKD into a larger fraction of the telecom and datacom network.”

Taro Shimada, corporate senior vice president and chief digital officer of Toshiba Corporation comments, “Toshiba has invested in quantum technology R&D in the UK for over two decades. This latest advancement is highly significant, as it will allow us to manufacture and deliver QKD in much larger quantities. It is an important milestone towards our vision of building a platform for quantum-safe communications based upon ubiquitous quantum security devices.”

Part of the work was funded by the Innovate UK Collaborative R&D Project AQuaSeC, through the Industrial Strategy Challenge Fund. The details of the advancement are published in the scientific journal, Nature Photonics.

Toshiba has developed the first complete QKD prototype in which quantum photonic chips of different functionality are deployed. Random bits for preparing and measuring the qubits are produced in quantum random number generator (QRNG) chips and converted in real-time into high-speed modulation patterns for the chip-based QKD transmitter (QTx) and receiver (QRx) using field-programmable gate arrays (FPGAs).  Photons are detected using fast-gated single photon detectors. Sifting, photon statistics evaluation, time synchronisation and phase stabilisation are done via a 10 Gb/s optical link between the FPGA cores, enabling autonomous operation over extended periods of time. As part of the demonstration, the chip QKD system was interfaced with a commercial encryptor, allowing secure data transfer with a bit rate up to 100 Gb/s.

In June 2021, Toshiba, in conjunction with Cambridge Research Laboratory, announced it had successfully completed  Europe’s first demonstration of quantum communications over optical fibres exceeding 600 km.

For more information, visit www.toshiba.com