Ph.D. Defense: Uday Saha

Tuesday, September 13, 2022
10:00 a.m.
ERF 1207
Maria Hoo
301 405 3681



NAME:  Uday Saha

Prof. Edo Waks (Chair)
Prof. Thomas E. Murphy
Prof. Agisilaos Iliadis
Prof. Avik Dutt
Prof. John Cumings (Dean’s Representative)

Date/time: Tuesday, September 13th, 2022 at 10 AM  
Location:  ERF 1207

Title:  Quantum Modem and Router for Quantum Internet 

Like the internet, quantum internet can change the world by connecting quantum computers over long distances. This connectivity can revolutionize different industries like banking, healthcare, and data analytics that utilize quantum computing and simulations. Additionally, it would enable us to connect multiple small quantum computers into powerful distributed quantum computers that can solve problems of significant societal impact.

Despite the rise of excellent quantum computers, we don't yet have the core technologies to connect them. This is because modems and routers we use to connect classical computers don't work for quantum information. They destroy the coherence and entanglement of quantum information, which is vital for connecting quantum computers.

In my thesis, I developed a quantum modem and router that can connect quantum computers and create a scalable quantum network. I have conceived the modem and router for the trapped ion quantum computers, the most promising quantum computing platform. However, we can easily use my developed concepts to connect different quantum computing platforms.

I accomplished a quantum modem that provides an interface between a quantum computer and a fiber-optic network by generating telecom photons from the computer. I used a two-stage quantum frequency conversion scheme to realize the quantum modem. By calculating the second-order correlation function, I experimentally verified single-photon characteristics retained after the two-stage quantum frequency conversion process. Telecom single photons generated by quantum modem can carry quantum information from ions over long distances. This will allow a long-distance quantum network to realize the quantum internet.

On the other hand, I implemented a quantum router with photonic integrated circuits. Utilizing the thermo-optic property, I route photons from a trapped barium ion into different output ports of the quantum router in a programmable manner. This router can connect multiple quantum computers on-demand and in a scalable way. We are the first group to demonstrate a quantum modem and router working together. This demonstration could lead to a scalable quantum network where photons from different quantum computers can be interfered with a programmable photonic chip to herald entanglement.

Additionally, I developed visible photonic circuits for quantum data centers. In a quantum data center, there can be multiple trapped ion quantum computers that need to be connected. For this purpose, I designed a photonic circuit on a thin-film lithium niobate platform that can entangle two trapped ion quantum computers with 99.9% fidelity. Apart from achieving high fidelity entanglement, the circuit can achieve any polarization-independent power splitting ratio, which can have extensive use in integrated photonic technology.

Finally, I invented a multiplexing scheme by which we can send quantum information from multiple quantum computers using a single fiber-optic cable. That will increase the channel capacity and multiple quantum computers can communicate through the same channel. By encoding quantum information into the different wavelengths of photons, I devised my idea of multiplexing quantum information.

Audience: Graduate  Faculty 

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