A quantum internet is a quantum network in which the processors are located at different geographical locations. Our goal is to develop the technology to enable quantum communication between any two places on earth. One application of such a quantum internet is to provide a fundamentally secure way of communication, in which privacy is guaranteed by the laws of physics.
Quantum processors can be connected into a quantum network in order to assemble a large quantum computing cluster. This approach is called networked quantum computing and offers a natural path towards scalability, complementary to the quantum computing work described in the previous chapter. Combining a quantum internet and a networked quantum computer allows remote users/providers to perform secure quantum computing ‘in the cloud’.
Quantum network protocols and applications
Long-term goal: Development of a full control stack and novel applications for a quantum internet.
2019 Research Highlights:
- We developed a so-called link layer protocol that brings the phenomenon of ‘quantum entanglement’ from a physics experiment towards a real-world quantum network. The link layer protocol allows to reliably generate entanglement between two network nodes connected by a direct physical link, without the need to know which quantum hardware system is in the box. The work was presented at ACM SIGCOMM. Read more
- We co-organized a pan-European hackathon which simultaneously took place in Paris, Genève, Sarajevo, Padua, and Delft. The hackathon was organized within the framework of the EU-funded Quantum Internet Alliance (QIA). It attracted ca. 100 participants who took on various different challenges related to first applications that use quantum physics to secure online communications.
- We have analyzed different protocols through which near-term experiments with NV centers can overcome the limitations of direct transmission. This work points towards first proof-of-principle experiments in which entanglement generation between end nodes connected by high-loss channels can be sped up. We report on this in Phys. Rev. A.
Quantum network experiments
Long-term goal: Experimental demonstrations, some of which already compatible with existing telecom infrastructure, that push the frontier of quantum networking and yield new techniques and insights.
2019 Research Highlights:
- Europe aims to deploy a quantum communication network providing quantum key distribution (QKD) as a service. It is possible to benefit from existing infrastructure by having the quantum communication signal coexisting with the classical one over the same fiber. This will help to minimize operating costs and hence facilitate deployment. We showed that measurement-device independent (MDI) QKD can operate simultaneously with classical communication channels operating at around 1550 nm wavelength and over 40 km of spooled fiber, with projected communication. The similarity of MDI-QKD with quantum repeaters suggests that classical and generalized quantum networks can co-exist on the same fiber infrastructure. The work was published in Quantum Sci. Technol.
- We demonstrated that conversion of single photons emitted by NV center qubits from the visible to the telecom band (where losses in fibers are minimal) preserves entanglement of the photon with the qubit. This is a key result for extending quantum networks based on diamond-based quantum processors to large distances. This work was published in Phys. Rev. Lett.
- We reported on the storage and reemission of heralded telecommunication-wavelength photons using a crystal waveguide in Phys. Rev. Applied. Despite currently limited storage time and efficiency, this demonstration represents an important step toward quantum networks that operate in the telecommunication band and the development of integrated (on-chip) quantum technology using industry-standard crystals.
Quantum processors for quantum networks
Long-term goal: Develop and exploit multi-qubit quantum processors for use in quantum internet and networked computing, with current focus on diamond-based spin qubits.
2019 Research Highlights:
- We demonstrated a fully controllable chip with ten qubits that can store quantum information for up to one minute (Phys. Rev. X). Controlling such a large number of qubits with long memory times is an important step forward for chip-based qubits and might pave the way to large multi-qubit quantum systems. Read more
- We developed non-destructive measurements of a joint property of multiple qubits, namely their parity (Phys. Rev. Lett.) We explicitly showed that these measurements can be applied repeatedly to three nuclear spin qubits without destroying their joint quantum state. These measurements are key ingredients for error correction and measurement-based computing schemes.
- Using novel quantum control techniques, we succeeded in imaging 27 nuclear spins surrounding an NV center spin qubit. These unprecedented control and imaging capabilities pave the way for extending local quantum registers in network nodes well beyond 10 nuclear spins. Our findings were published in Nature.