Kick-off workshop for ASPIRE Quantum program between the University of Tokyo and the University of Chicago on July 26, 2024. The workshop will be held in a hybrid mode with in-person attendance at Sanjo Conference Hall in the University of Tokyo, Hongo campus, and Zoom connection.
The Zoom connection is provided at Videoconference and Timetable on the left panel.
Please note that Sanjo Conference Hall will be opened at 9:00.
In this talk we will discuss to what extent entanglement is a "feelable" (or efficiently observable) quantity of quantum systems. Inspired by recent work of Gheorghiu and Hoban, we define a new notion which we call "pseudoentanglement", which are ensembles of efficiently constructible quantum states which hide their entanglement entropy. We show such states exist in the strongest form possible while simultaneously being pseudorandom states. Consequently, we prove that there is no efficient algorithm for measuring the entanglement of an unknown quantum state, under standard cryptographic assumptions. We will talk about applications of this construction to diverse areas of physics and computer science.
Nuclear spins interact weakly with their environment and therefore exhibit long coherence times. This has led to their use as memory qubits in quantum information platforms, where they are controlled via electromagnetic waves. Scaling up such platforms comes with challenges in terms of power efficiency, as well as cross-talk between devices. Here, we demonstrate coherent control of a single nuclear spin using surface acoustic waves. We use mechanically driven Ramsey and spin-echo sequences to show that the nuclear spin retains its excellent coherence properties. We estimate that this approach requires 2–3 orders of magnitude less power than more conventional control methods. Furthermore, this technique is scalable because of the possibility of guiding acoustic waves and reduced cross-talk between different acoustic channels. This work demonstrates the use of mechanical waves for complex quantum control sequences, offers an advantageous alternative to the standard electromagnetic control of nuclear spins, and opens prospects for incorporating nuclear spins in mechanically interfaced hybrid quantum architectures.
We have developed two spectroscopic methods: Magnetization State Tomography, which measures the Wigner function of magnetization fluctuations, and Magnetization Parametric Projection Measurement, which selectively amplifies the phase information of magnetization. As applications of these methods, we introduce the realization of magnetization squeezing, the direct measurement of magnetization parametric oscillation, and the discovery of hidden coherence in magnetization.