Uniting Precision Measurement and Quantum Control

Takefumi Miyoshi, Keisuke Koike, Shinichi Morisaka +4 more

This paper proposes a scalable control device architecture for trapped-ion quantum computers based on microwave quantum control. While microwave control of trapped-ion qubits offers high gate fidelity, it requires high-precision and scalable microwave control devices. In the control devices for microwavebased trapped-ion quantum computers, three types of signals need to be managed: (1) wideband microwaves with low phase noise for quantum gate operations, (2) numerous signals with sub-microsecond voltage changes to implement the quantum charge-coupled device (QCCD) architecture, and (3) triggers to synchronize measurement instruments. The proposed architecture combines heterogeneous control devices tailored to these three types of signals to achieve the required precision and scalability at a practical cost. The system features a shared sequencer that can manage all units uniformly, ensuring scalability and reducing development costs. To correctly execute the control sequences, it is necessary to align the operating timing of each unit. In the proposed system, each unit maintains a common time and independently issues events by referring to this time. High-precision time synchronization protocols based on IEEE1588 can be used for time synchronization. In addition to that, multiple control devices can be expanded by combining fine-grained synchronization mechanisms using time synchronization and shared reference signals. This paper details the specifications required for trappedion quantum computers using microwaves and proposes an architecture that meets these specifications.

H. Ezawa, Yoshimasa Murayama

Liangyu Ding, Qiuxin Zhang, ZHU ChenHao +3 more

Measuring physical quantities with unprecedented precision is one of the most important paradigms to extend our fundamental understanding of nature. With the development of new quantum techniques, quantum systems have become a promising platform along the path to pursue higher accuracy and stability of measurement, while the classical methods are approaching their own limitation. Owing to its high stability, long coherence time and good controllability of quantum states, the trapped ion system has attracted much attention as a promising platform for quantum metrology. Recent progress on quantum control of trapped ions in both the scientific and technological aspects greatly advance the potential applications in precision measurement of various physical quantities. The invention of optical comb with ultra-stable laser brings us a new approach to develop a clock working on optical frequency, and features a much higher precision than microwave. This achievement has the potential reform the definition of the basic unit of the international system of units in the near future. New methods of dynamic decoupling or preparing special dressed states significantly extend the coherence time, such that an ultra-sensitive detection of magnetic field can be achieved. By introducing a spin-dependent kick in the phase space, one may also realize rotation measurement with trapped ions and obtain high accuracy with a chip-size apparatus. In this short review, we introduce the principles and designs of optical clock, magnetometer and gyroscope based on trapped ion systems. Owing to its unique features, this platform presents many advantages which can help improving sensitivity and stability, as well as building transportable devices.

Gerard J Milburn

Ken Krechmer

A classic (i.e., physical) measurement result is a quantity (e.g., 6.9 seconds, 13 metres, 0.17 grams, etc.). A quantity is the product of two terms: a numerical value and a unit. The unit when calibrated to a standard has a +/- precision. In quantum mechanics (QM) a wave function produces a distribution of eigenvalues of unity eigenvectors. Each product of one eigenvalue of eigenvectors also represents one measurement result quantity. In a QM measurement process this distribution of quantities appears to collapse into one classic measurement result quantity (one numerical value and a unit). In classic measurement result quantities, (without noise or distortion) the numerical value of an observable appears fixed over repetitive measurements and the units have a precision relative to a standard. However in a QM measurement result quantity, the eigenvalues have Heisenberg's uncertainty and the eigenvectors are unity. This paper formally develops and verifies that both the QM and classic measurement result quantities are equal products and the classic unit precision is equal to the QM eigenvalue uncertainty.

Michael Hatridge