North Carolina State University researchers and scientists from the Massachusetts Institute of Technology have developed a technique for using quantum sensors' power. Using the protocol, sensor designers may be able to precisely adjust quantum systems to detect desired signals, producing far more sensitive sensors than conventional ones. This research was published in the journal Quantum.
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Quantum sensing shows promise for more powerful sensing capability that can approach the fundamental limit set by the law of quantum mechanics, but the challenge lies in being able to direct these sensors to find the signals we want.
Yuan Liu, Assistant Professor and Study Corresponding Author, Department of Electrical and Computer Engineering, North Carolina State University
Liu was formerly a Postdoctoral Researcher at MIT.
Our idea was inspired by classical signal processing filter design principles that are routinely used by electrical engineers. We generalized these filter designs to quantum sensing systems, which allows us to ‘fine-tune’ what is essentially an infinite dimensional quantum system by coupling it to a simple two-level quantum system.
Yuan Liu, Assistant Professor and Study Corresponding Author, Department of Electrical and Computer Engineering, North Carolina State University
The researchers created an algorithmic framework connecting a bosonic oscillator and a qubit. Quantum bits, also known as qubits, are the equivalent of bits in classical computing in quantum computing. They can store quantum information and are limited to two superpositions of basis states: ├ |0⟩ and ├ |1⟩.
Consider the motion of a pendulum to understand the quantum analog of classical oscillators or bosonic oscillators. While they have many of the same characteristics as classical oscillators, their states are infinite-dimensional systems rather than a linear combination of just two base states.
Manipulating the quantum state of an infinite-dimensional sensor is complicated, so we begin by simplifying the question. Instead of trying to figure out amounts of our targets, we just ask a decision question: whether the target has property X. Then we can design the manipulation of the oscillator to reflect that question.
Yuan Liu, Assistant Professor and Study Corresponding Author, Department of Electrical and Computer Engineering, North Carolina State University
Adjusting the coupling to the two-dimensional qubit allows the infinite-dimensional sensor to be tuned to a desired signal. The qubit state is measured for readout after the data are encoded using interferometry.
“This coupling gives us a handle on the bosonic oscillator, so we could use a polynomial function – math that describes waveforms – to engineer the oscillator’s wave function to take a particular shape, thus attuning the sensor to the target of interest,” Liu said.
Liu added, “Once the signal happens, we undo the shaping, which creates interference in the infinite-dimensional system that comes back as a readable result – a polynomial function determined by the original polynomial transformation of the oscillator and the underlying signal in the qubit’s two-level system. In other words, we end up with a ‘yes’ or ‘no’ answer to the question of whether the thing we’re looking for is there. And the best part is that we only need to measure the qubit once to extract an answer – it’s a ‘single-shot’ measurement.”
According to the researchers, the work offers a broad foundation for creating quantum sensing protocols that may be used for various quantum sensors.
Liu explained, “Our work is useful because it utilizes readily available quantum resources in leading quantum hardware (including trapped ions, superconducting platform, and neutral atoms) in a fairly simple way. This approach serves as an alarm or indicator that a signal is there, without requiring costly repeated measurements. It is a powerful way to extract useful information efficiently from an infinite dimensional system.”
The Army Research Office and the US Department of Energy funded the study. Co-first authors include Jasmine Sinanan-Singh and Gabriel Mintzer, both graduate students at MIT. Isaac L. Chuang, Professor of Physics and Electrical Engineering and Computer Science at MIT, also contributed to the research.
Journal Reference:
Sinanan, -S. J., (2024) Single-shot Quantum Signal Processing Interferometry. Quantum. doi.org/10.22331/q-2024-07-30-1427.