Quantum sensors detect signals that classical sensors cannot measure
Quantum sensing that measures qubits, the foundation of quantum technology
For the time being, quantum sensors and classical sensors will be used complementarily


Quantum mechanics, which was established in the 20th century, led to the creation of semiconductors and rapidly advanced human technological standards. Recently, the commercialization potential of quantum technologies such as quantum computing, quantum communication, quantum simulation, and quantum sensing has emerged.

Professor Lee Dong-heon of the Department of Physics at Korea University contributed an article titled “Quantum Sensor Research Trends and Utilization Prospects” to the 1960th issue of the “Weekly Technology Trends of the Institute of Information & Communications Technology Planning and Evaluation (IITP),” in which he introduced the basic measurement principles, use cases, and domestic and international research and market trends of quantum sensing.

According to Professor Lee Dong-heon, quantum sensing is a technology that generally measures physical quantities such as time and magnetic fields using quantum systems such as qubits, and is a sensing and imaging technology that accurately measures minute signals that cannot be measured with classical systems by utilizing the unique characteristics of quantum systems.

The professor emphasized that precise measurement of quantum states such as qubits is the foundation of all quantum technologies, and that advances in quantum sensing can serve as a stepping stone to the realization of mid- to long-term large-scale technologies such as quantum computing and quantum communications.

In addition, it can be utilized in various sensor fields, and can have wide-ranging ripple effects across various fields such as ICT, industry, medicine, and defense, he added.

◇ Principles and processes of quantum sensing

The quantum sensing process is divided into three stages: △ sensor initialization, △ interaction with the target signal, and △ measurement of the final state of the sensor. The professor explained that the key is how precisely one can measure the minute quantum phase changes (Quantum Phase Accumulation) that occur through the interaction between the sensor and the target signal.

A qubit is a two-level system consisting of quantum states of 0 and 1, and can create an arbitrary superposition state between 0 and 1 through various gate controls.

The qubit state changes over time due to a signal from an external target, and by measuring the relative phase change between 0 and 1, information such as the size and frequency of the target signal is obtained. In addition, since the quantum state is given probabilistically, this is repeated multiple times to obtain a meaningful average value.

Quantum sensing is accomplished through a seven-step process. First, ▲ sensor qubit initialization (state 0) ▲ conversion to an arbitrary superposition state (state where 0 and 1 are superimposed 50:50) ▲ change in qubit state due to interaction with a signal ▲ conversion to a state where the qubit state can be read ▲ probabilistic measurement of the 0 and 1 qubit states through projection readout.

And ▲by repeating the previous process, a meaningful average value is obtained, and ▲the signal size, direction, frequency, etc. are estimated from the measured average value. The professor said that different types of sensing protocols are used in processes ② to ④ depending on the frequency band of the target signal.

◇ Quantum sensors to replace classical sensors

Professor Lee Dong-heon said that the types of quantum sensors and the physical quantities that can be measured using them are very diverse, and that there are quantum sensors optimized for specific physical quantities, citing gravimeters, gyroscopes, and magnetometers as examples.

Gravimeters that measure changes in gravitational acceleration are divided into optical interferometers and atomic interferometers. Quantum gravity sensors such as atomic interferometers can be used to create small, portable, and movable gravimeters that can precisely measure small changes in gravitational acceleration over a local area.

Gyroscopes used to measure rotation angle and rotational velocity are mostly MEMS (Micro Electro Mechanical Systems) or ring laser type sensors. Recently, quantum sensors based on atoms and spin qubits are being studied and are attracting attention as a replacement for these.

A magnetometer is a device used to measure the magnitude and direction of a magnetic field. Quantum magnetometers include the SQUID (Superconducting Quantum Interface Device), the Atomic Vapor Cell, and the Diamond NV Center.

Since they simultaneously satisfy high spatial resolution and high magnetic field sensitivity, they are expected to be utilized in various fields such as ▲inertial measurement units (IMUs) ▲magnetoencephalography (MEG) ▲nano magnetic resonance imaging (MRI).

Additionally, the professor said that portable atomic gravity sensors, helmet-shaped MEG devices consisting of atomic vapor cells, dynamic nuclear polarization (DNP) devices used for NMR and MRI measurements, and chip-shaped atomic clocks have been commercialized.

◇ Current status of domestic and international quantum technology investment

As interest in quantum sensing and other quantum technologies has surged, the scale of domestic and international government-funded research funding and corporate R&D investment has also increased rapidly in recent years.

The United States has decided to invest approximately 1.5 trillion won in the first five years of the National Quantum Initiative across all areas of quantum technology over the next ten years starting in 2019.

The European Union (EU) has decided to support research costs totaling 1.3 trillion won over 10 years starting in 2018 through the 'Quantum Technologies Flagship' policy. Currently, a total of four quantum sensing projects are in progress: ▲Light-based quantum clock ▲Atomic vapor cell-based angular velocity/magnetic field/clock ▲Diamond NV center-based MRI imaging ▲Diamond NV center-based magnetic/electric field/temperature/pressure sensor.

The UK has been providing support totaling 400 billion won over 10 years since 2014 through the 'Quantum Technology Hub' and is carrying out a total of 12 quantum sensing projects, including gravimeters, magnetometers, gyroscopes, atomic clocks, and quantum imaging.

In China, a total of 12 trillion won in support will be provided to quantum technology in general, starting with the establishment of the National Institute of Quantum Information Science, which is scheduled to open this year.

In Korea, starting in 2019, a total of about 100 billion won in support will be provided over five years across all fields of quantum technology under the leadership of the research foundation and IITP, and five quantum sensing projects are in progress, including gravimeters, magnetometers, imaging, and light sources. In addition, it is expected that the scale of research funding will be expanded based on the level of securing the initial ecosystem in the quantum information field and domestic and international research trends.

◇ Quantum sensors to be used complementarily with classical sensors for the time being

According to Inside Quantum Technology, the global quantum sensor market size, which was approximately KRW 1 trillion in 2019, is expected to grow to approximately KRW 2.5 trillion in 2028, 10 years later.

While quantum magnetometers and atomic clocks are expected to lead the quantum sensor market, demand for quantum sensors is expected to increase across industries, especially in navigation/transportation and medicine.

Professor Lee Dong-heon said, “Quantum sensors are capable of ultra-precision sensing, but they require high-level control technology to sense while maintaining the fragile quantum characteristics,” and “It will take a considerable amount of time until true quantum sensors are commercialized.”

Professor Lee predicted that quantum sensors will be used as an innovative technology in the market occupied by existing sensors for the time being, targeting niche markets that require new platforms, miniaturization, and low magnetic fields, or will be used complementarily with existing sensors.

The professor said, “In the history of semiconductor development, sensors such as photocells were developed first and utilized in various fields before commercial computers were released,” and added, “Quantum sensors can serve as a stepping stone to the realization of other quantum technologies.”