Dear Fellow Quantum Mechanicians

Jeremy Bernstein

This is an open letter on the nature of the quantum theory.

P. E. Toschek

Abstract Dear Chairmen Profs. Herschbach and Toennies, dear organizers Profs. Schmidt-Böcking and Friedrich, dear Colleagues, dear Ladies and Gentlemen. The occasion for our gathering today in this location is a truly historic one: the centenary of the first quantitative experiment with molecular beams, a technique that would enable, in 1922, the first convincing proof of quantum mechanics—the fundamental theory of light and matter—and to give due honor to the pioneer physicist who developed this technique: Otto Stern.

Ching-Yao Huang, Wai-Kei Mak

In current quantum devices, physical qubits are not fully connected so that two-qubit interaction can only be performed between specific pairs of physical qubits. To execute a quantum circuit, it is necessary to transform it into a functionally equivalent one that respects the constraints imposed by the target architecture. Quantum circuit transformation inevitably introduces additional gates which reduces the fidelity of the circuit. Therefore, it is important that the transformation method completes the transformation with minimal overheads. Quantum circuit transformation consists of two steps, initial mapping and qubit routing, and here we propose a DEAR (Dynamically-Extract-and-Route) framework to solve the qubit routing problem. A key insight of DEAR is that by maintaining a sufficient lookahead ability all the time, we can make much better routing decisions while effectively controlling the runtime. In our DEAR framework, we periodically extract a subcircuit by identifying a set of remaining gates that should be executed earlier than the others, and then applies A* search to determine how to insert a sequence of additional SWAP and BRIDGE operations into the subcircuit to obtain a high quality routing solution with minimum number of additional gates. In this work, we consider the insertion of both SWAP and BRIDGE operations while most previous works deal with SWAP insertion only. We evaluate our approach with four benchmark sets with different characterization on IBM Tokyo. The experimental results show that our approach outperforms the state-of-the-art work utilizing SWAP and BRIDGE insertion with 19.1% and 77.5% average reduction in the number of additional gates and runtime, respectively, starting from the same initial mapping. We also performed experiments on larger quantum devices such as Google Sycamore and IBM Rochester both with 53 physical qubits that have largely different architectures from one another and from IBM Tokyo. Again, DEAR was much faster and required significantly less amount of additional gates.

Ross Barrett, Pier Paolo Delsanto