In March 2023, the Indian Ministry of Communications announced the first operational quantum communication link in New Delhi. This communication link transmits qubits – information encoded in quantum states of light – instead of classical bits, which ensures inherently secure transmission as any attempt to eavesdrop is not only detectable, but also destroys the information being shared by collapsing the superposition state of the qubit. This implicit confidentiality and integrity is of immense value to the security industry, and thus makes quantum communications one of the most commercially possible applications of quantum photonics.
While there is academic work being done to develop QSDC (Quantum Secure Direct Communication) and QSS (Quantum Secret Sharing), most quantum communication network prototypes today implement Quantum Key Distribution (QKD), in which cryptographic keys are encoded in entangled photons and transmitted.
- China is home to the largest stable QKD network, which, established back in 2017, consists of a 2000 kilometre network running through Beijing, Jinan, Hefei and Shanghai, and an additional 2600 kilometre satellite link. This network services hundreds of Chinese banks, state entities, and industries. While China leads the QKD race comfortably, there is significant investment and effort being consolidated globally too. The endeavour is collaborative, requiring muscle from governments, academics, and companies.
- In the United States, Toshiba and the Chicago Quantum Exchange (CQE) recently extended their 144 kilometre QKD loop by an additional 56 kilometres.
- In India in March 2023, Scientists at RRI demonstrated QKD between a stationary and a moving source, which is the principle upon which secure satellite communication can be built.
- The AWS Center for Quantum Networking (CQN), Singapore, in collaboration with the Centre for Quantum Technologies (CQT), Horizon Quantum Computing, and Fortinet recently implemented a QKD network in a customer environment in Singapore.
- Japan, which has had the Tokyo QKD Network since 2011, is now developing a WAN of over 100 quantum cryptographic devices; this effort is being led by Toshiba.
- Russian state and industry projects have defined a quantum network testbed, consisting of the cities St. Petersburg, Moscow, Kazan, and Samara, where several academic institutions as well as industry partners are developing QKD technology.
- In Canada The Quantum Encryption and Science Satellite (QEYSSat) mission will demonstrate quantum key distribution (QKD) in space ( 2024-25)
- In the UK, BT and Toshiba Europe Limited have an industrial deployment of a quantum-secure network, transmitting between the National Composites Centre (NCC), the UK’s world-leading composite research and development facility, and the Centre for Modelling & Simulation (CFMS), a not-for-profit research organisation that pioneers new digital engineering capabilities.
- The OpenQKD Project by the European Union has participation from Austria, Czech Republic, France, Germany, Greece, Italy, Netherlands, Poland, Spain, Switzerland and the UK. There are four main testbeds in Berlin, Madrid, Poznan and Vienna.
This is a non-exhaustive list of some of the QKD efforts around the globe.
A key factor in the success of photonics-based quantum communication is how well it integrates with classical communication systems. Quantum technology is predicted to enable 6G wireless communication networks in achieving higher speeds, enhanced energy and cost efficiency, wider coverage, autonomy and intelligence, and most prominently, increased security. Telecom giants from across the globe are looking at how 5G and 6G bottlenecks can be overcome using quantum technology.
The use of photonics for the design of the scalable quantum computer is also one of the hardware approaches being considered for computing. Photons are a popular qubit modality upon which quantum computing hardware is being designed.
- In January 2023 , the Canadian government announced a new federal investment of 40 million CAD to Xanadu, to build and commercialise a photonics-based quantum computer.
- In February 2023 PsiQuantum received a fund from the British government to develop single photon detectors for photonic quantum information processing.
- India has a start-up Quanfluence which is also focusing on a Photonics based Quantum Computer, but at a fraction of the cost estimate of the efforts by other companies.
- Other companies worldwide, such as British ORCA Computing, Parisian Quandela, Israeli Quantum Source, are also involved in developing a photonics-based quantum computer.
Compared to other options such as superconducting qubits, trapped ions, neutral atoms, etc., quantum optical circuits offer higher fidelities, and faster gate speeds. Most importantly, they do not directly require cryogenics, and are easy to integrate with existing semiconductor technology used in classical photonics. The biggest challenge foreseen is scalability; with issues like photon absorption and photonic qubit storage and memory, the application of quantum computers to complex problems could take a while. To efficiently solve complex problems in areas like drug discovery and supply chain optimization, quantum computers will have to consist of millions of reliable, physical qubits. Photonic quantum computers are also advantageous because they easily interface with quantum communication links.
Photonics also offers an alternate view to compute scalability. through an inter-network of several quantum devices capable of securely communicating with each other. This can enable connecting several smaller, less computationally powerful quantum computers consolidating their resources. Placing quantum communication devices up in space could pave the way for a space-based quantum internet. Research is being conducted to facilitate the use of the quantum internet to create sensor networks that can be used in the domains of quantum sensing, metrology, and imaging.
Photonics based Quantum sensing involves the use of quantum states of photons to detect minute changes in the environment. The idea of using light as a probe is not new, but recently, quantum optical properties like entanglement and squeezing are being studied to achieve orders-of-magnitude improvements in precision. Photonic quantum sensors may be used in areas such as gravitational wave detection, quantum radar, in complex biological systems. Quantum biophotonics is an emergent field which focuses on making sensitive, reliable and traceable measurements in an ever-changing bio-environment.
Quantum photonics may be used to model complex chemical systems too! Photonic quantum simulators are single photon systems that emulate other quantum systems. The application of photonic quantum simulation extends beyond chemistry, to fields like condensed matter physics and medicine. Quantum simulation can enable fundamental insights into hard problems that are classically intractable, and is hence important to public and private entities around the world.
Indeed, quantum photonics is applicable in a wide range of domains. It lies at the core of several upcoming industries, and has the potential to disrupt existing ones.
By Padmapriya Mohan & Reena Dayal
