Quantum Networking with Diamond Nanophotonics

A display of SiV molecules moving across circuits

Quantum Networks with SiV Centers

 

A SiV moleculeQuantum networks are an exciting complement to quantum computing, as they would enable us to send quantum states and share entanglement over long distances, and enable applications ranging from quantum key distribution to connecting future quantum computers and quantum sensing of astronomical sources. In this lab, we use the silicon-vacancy (SiV) defect in diamond as an ideal platform to realize deployed real-world quantum networks and explore quantum information applications of distributing entanglement via light.

 

Intrinsic Two-Qubit Solid-State Qubit Platform

 

SiVs are created when two carbon atoms in diamond are replaced with a silicon atom, allowing it to intrinsically contain two qubits in the form of an electron spin and a long-lived nuclear spin qubit (> 2 seconds) from the 29Si isotope; both spins are fully controllable into entangled two-qubit states with high fidelity (>99%) using microwave pulses. 

 

Demonstration of crystal cavity

 

The SiV lives in a fiber-coupled nanophotonic cavity to enhance its interaction with light, allowing incoming light to be entangled with the electron spin qubit. Our platform enjoys the advantageous combination of being able to generate entanglement that is both high-fidelity and high-efficiency, as well as scalability from the ability to manufacture hundreds of cavities on a single chip. 

 

Deployed Quantum Networks

We have demonstrated several key milestones in deployed quantum networking on our platform, including quantum frequency conversion to the low-loss 1350 nm telecom band, storing an encoded photon sent from MIT Lincoln Labs over 50 km of deployed fiber onto the SiV memory, and entangling two SiVs in separate labs over 35 km of fiber around the Boston area and storing the entanglement for more than 1 second.

 

Our main research goals focus on pushing the SiV platform to realize useful applications of near-term quantum networks and entanglement.

 

 

Ongoing research directions include:

  1. Can we build a deployable quantum repeater node to enable long distance quantum networks?
  2. Can we use two entangled nodes at a distance to perform interferometry of faint astronomical sources more efficiently?
  3. Can we use photons entangled with our SiV qubits to enable a client with only measurement capabilities to perform quantum computation without leaking the contents of the computation?

 

 

Recent Publications:

  1. Entanglement of Nanophotonic Quantum Memory Nodes in a Telecom Network, (arXiv)
    1. We entangled two electron and nuclear spins located in different labs with entanglement lasting over 1 second. By performing frequency conversion to the low-loss telecom band, we extend the entanglement length to 40 km of spooled fiber and over 35 km of deployed fiber in the Boston area.
  2. Telecom Networking with a Diamond Quantum Memory, PRX Quantum (2024) (arXiv)
    1. We demonstrated bidirectional quantum frequency conversion of single photons from the SiV’s native wavelength of 737 nm to the low-loss 1350 nm telecom band and vice versa while maintaining low noise and high indistinguishability. We used this to store telecom pulses sent over a 50 km deployed fiber link from MIT Lincoln Lab onto an SiV at Harvard with a storage fidelity of 87%.
    2. Distance between nodes
  3. Robust multi-qubit quantum network node with integrated error detection, Science (2022) (arXiv)
    1. We expanded the SiV system to a two-qubit register using the 29Si nuclear spin as a memory qubit lasting over 2 seconds. With a highly-strained device, we entangled the electron spin with a photon at 1.5K and implemented the PHONE gate to perform photon-nucleus entanglement with integrated error detection.
    2. Fidelity and storage time
  4. Efficient Source of Shaped Single Photons Based on an Integrated Diamond Nanophotonic System, Phys. Rev. Lett. (2022) (arXiv)
    1. ​​​​​​​We created a new cavity design optimized for photon outcoupling efficiency and used the SiV as a deterministic single-photon source. We showed arbitrarily-shaped photon pulses with high efficiency (14.9%) and high purity (g(2)(0) = 0.0168), enabling the generation of streams of up to 11 consecutive photons in-fiber.
    2. Photon counts over time
  5. Experimental demonstration of memory-enhanced quantum communication, Nature (2020) (arXiv)
    1. ​​​​​​​We stored two time separated phase-encoded photon pulses onto the SiV, and then read out the combined parity state of the encoded bits. This implements an asynchronous Bell-state measurement, a key component of quantum repeaters, giving us quantum communication rates surpassing loss-equivalent direct transmission.
    2. Bell States​​​​​​​