A special class of sensors leverages quantum properties to measure tiny signals at levels that would be impossible using classical sensors alone. These groundbreaking quantum sensors combine principles of quantum mechanics with advanced technology to achieve unprecedented sensitivity and accuracy.
Such quantum sensors are currently being used to study the inner workings of cells, revealing intricate biological processes that were previously shrouded in mystery, and the outer depths of our universe, allowing scientists to explore cosmic phenomena with unparalleled precision.
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By harnessing the unique behaviors of quantum particles, researchers are making significant strides in various fields, from biomedical research to astrophysics, fundamentally transforming our understanding of both microscopic and macroscopic scales.
Solid-state quantum sensors show great potential as they can work at room temperature. However, most of these sensors currently measure only one aspect at a time, like the magnetic field, temperature, or strain in a material. Attempting to measure both the magnetic field and temperature simultaneously causes interference and makes the readings unreliable.
Now, MIT researchers have excitingly developed a groundbreaking method to measure multiple physical quantities simultaneously using a solid-state quantum sensor. They achieved this remarkable feat by harnessing the power of entanglement, where particles are beautifully intertwined in a single quantum state.
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In a recent study, the team tested this method with a widely used quantum sensor at room temperature, measuring the amplitude, frequency, and phase of a microwave field in one go. They found that this method is more effective than measuring each property one by one or using traditional sensors.
The researchers enthusiastically suggest that this innovative approach could empower quantum sensors, potentially revolutionizing our understanding of atomic and electronic behaviors within materials and living systems, including cancer cells.
“Quantum multiparameter estimation has been mostly theoretical to date,” says co-lead author of the paper Takuya Isogawa, a graduate student in nuclear science and engineering.
Few experiments have demonstrated this, with most focusing on photons. We aimed to show multiparameter estimation in a more practical setup using a solid-state quantum sensor currently in use.
Joining Isogawa on the paper are co-lead authors Guoqing Wang, PhD ’23, and MIT PhD candidate Boning Li. Other authors include former MIT visiting students Zhiyao Hu and Ayumi Kanamoto; University of Tokyo PhD candidate Shunsuke Nishimura; Haidong Yuan, a professor at the Chinese University of Hong Kong; and Paola Cappellaro, MIT’s Ford Professor of Engineering and a member of the Research Laboratory of Electronics.
Quantum effects for measurement
Quantum sensors use quantum effects such as entanglement and superposition to measure changes in magnetic and electric fields, gravity, and acceleration. They can also track the activity of single molecules, which helps in studying biology and space, such as monitoring metabolites or enzymes in cells.
One useful sensor in biology uses nitrogen-vacancy (NV) centers in diamonds, in which a nitrogen atom replaces a carbon atom in the diamond lattice, creating a vacancy. This defect exhibits an electronic spin with transition frequencies that can be optically measured. The NV center’s spin state is highly sensitive to external factors like magnetic fields and temperature, allowing for precise measurements.
Unfortunately, different external effects change the energy resonances of the spin in similar ways, making it difficult to measure multiple effects at once. The result is that most solid-state quantum sensor applications measure a single physical quantity at one time.
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“If you can only measure one quantity at a time, you have to repeat experiments to measure quantities one by one,” Isogawa says. “That takes more time, which means less sensitivity. It also makes experiments more susceptible to errors.”
For their experiment, the researchers used NV centers inside a 5-square-millimeter diamond. They pointed a laser into the diamond and studied its fluorescence to make their measurements, a common approach for such sensors. To study the electronic spin of the NV center, they used a microwave antenna. To study the spin of the nitrogen atom, they used a radio frequency field.
“We used those two spins as two qubits,” Isogawa says, referring to the building blocks of quantum computing systems.
If one possesses a single qubit, only one measurement outcome can be obtained: specifically, either 0 or 1. This reflects the probability of the qubit being in the spin-up or spin-down state. This can be analogized to a coin toss, where the likelihood of landing on heads or tails is considered. By introducing two qubits, the parameters available for extraction are significantly enhanced.
The system worked because the spins of the sensor qubit and auxiliary qubit were entangled, a quantum property where the state of one particle is dependent on another. With one qubit, you get a binary outcome. With two, you get four possible outcomes with a total of three possible parameters.
The two qubits allowed researchers to measure those three quantities simultaneously using a technique known as the Bell state measurement.
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Other researchers had used the Bell state measurement at extremely low temperatures before, but the MIT researchers have brilliantly developed an innovative technique that enables measurement at room temperature. This exciting approach was first proposed by Wang, a talented graduate student in Professor Cappellaro’s lab, showcasing the remarkable progress being made in the field.
The researchers have compassionately developed an approach that allows them to simultaneously measure the amplitude, detuning, and phase of a microwave magnetic field.
They also express hope that this innovative method could be extended to measure electric fields, temperature, pressure, and strain, potentially aiding in numerous applications and improving our understanding of various phenomena.
“Measuring these parameters simultaneously can help us explore spin waves in materials, which is an important topic in condensed matter physics,” Isogawa says.
NV center sensors offer impressive spatial resolution and versatility, making it possible for them to measure a wide range of physical quantities with remarkable precision. Their adaptability truly opens up a world of possibilities for understanding and exploring the intricate details of our environment.
More Practical Quantum Sensing
The researchers believe this work is a key advancement for using solid-state quantum sensors to better understand biomedical research and materials. This is important because multiparameter estimation had not been successful in practical situations or with common quantum sensors.
What makes the NV center quantum sensors truly remarkable is their ability to operate at room temperature, making them incredibly suitable for exciting biological measurements and groundbreaking condensed matter physics experiments!
Although the researchers note that their sensor didn’t measure each quantity at the highest possible precision, they are excited about future work, where they aim to explore the potential for achieving even greater precision for each parameter.
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They intend to investigate the efficacy of their approach in characterizing heterogeneous materials.
“In an extremely uniform environment, you could use many different classical and quantum sensors and measure each physical quantity at the same time,” Isogawa says.
To effectively capture the exciting variations in physical quantities across different locations, you can leverage advanced high-spatial-resolution sensors that provide remarkable precision.
Additionally, there are incredible sensors available that can seamlessly measure multiple physical quantities at the same time, including temperature, pressure, and humidity. This technology opens up new possibilities for understanding our environment better than ever before!
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This approach presents significant advantages in such contexts, as it enables a thorough analysis of the environment, which enhances data collection and supports informed decision-making.
By employing advanced sensor technologies with high accuracy and sensitivity, one can effectively monitor dynamic conditions, ensuring that crucial changes are detected and understood in real-time, ultimately leading to more effective solutions and optimized performance across various applications.
Reference: https://news.mit.edu/2026/multitasking-quantum-sensors-can-measure-several-properties-0415
