Quantum Mechanics of Digital Excitation

Yutaka Shikano

The fundamental link between physics and computation leads to an exciting field of quantum computation. Since the birth of the programmable digital computer, random number generators in computers have been developed. In principle, the pseudo random number generators currently implemented in digital computers are predictable. However, a quantum random number generator is employed to ideally generate unpredictable random numbers. In this essay, we explain why a one-qubit quantum computer can be a quantum random number generator and how this leads to justifying the foundations of quantum mechanics.

David B. Tanner

M. A. Castellanos-Beltran, A. J. Sirois, D. I. Olaya +3 more

We present experimental measurements and analysis of leakage errors occurring during resonant digital control of a superconducting qubit. By increasing the amplitude of the digital pulse trains and therefore decreasing the duration of the control gates, from 100 to 40 ns for a π-gate, the leakage error rate measured per Clifford gate in a randomized benchmarking test increases from 4.3×10−4 to 2.4×10−3 and becomes the dominant source of single-qubit gate errors for our qubit; these error rates are 1–2 orders of magnitude larger than we measure when controlling the same qubit using traditional, shaped-analog signals. Simulations show the dominant leakage mechanism arises from the increased spectral power of the pulse trains at the frequency ω12 corresponding to excitations from the first excited state |1⟩ to the second excited state |2⟩. Our measurements demonstrate the fundamental limits to resonant digital control of low-anharmonicity qubits and outline the trade-off between reducing gate times while preserving gate fidelity. We discuss possible strategies for mitigating this issue in future digital control implementations.

Haoxuan Duan

This paper provides an overview of the basic principles, types, recent works, and applications of quantum digital signatures. The security of traditional digital signature schemes is compromised by the rise of quantum computing, leading to a need for post-quantum cryptography. Quantum digital signatures, which rely on the principles of quantum mechanics, offer a potential solution to this problem. This paper aims to provide a comprehensive overview of quantum digital signatures and post-quantum digital signatures. The paper introduces the basic principles of quantum mechanics, then explains key distribution in quantum digital signatures. The paper then provides a detailed description of both quantum and post-quantum digital signatures, including their differences and applications. Finally, the paper summarizes the main findings in the field, highlights potential future directions, and discusses challenges that humans must address. In addition, the paper examines the widespread applications of quantum digital signatures and post-quantum digital signatures in various fields such as Bitcoin, smart city blockchain, and finance. Finally, the paper summarizes the key findings in the field, highlighting potential future directions and discussing challenges that humans must address. Overall, this paper aims to provide readers with a comprehensive understanding of quantum digital signatures and post-quantum digital signatures and their applications in various domains.

Paul L. Kelley, Benjamin Lax, Peter E. Tannenwald