Beihang University Engineers Achieve Quantum Phonon Blocking Asymmetrically

Engineers at the School of Physics, Beihang University, Beijing, China, have demonstrated a system capable of blocking phonons asymmetrically, achieving a contrast ratio exceeding 55 decibels in directional control of these mechanical vibrations. The work details a quadratic optomechanical system where the behavior of phonons changes depending on the direction of excitation; single-phonon resonance induces conventional phonon blockade in one direction, while two-phonon resonance facilitates phonon-induced tunneling in the other. Researchers revealed that increasing thermal noise reverses the statistics from bunching to antibunching in one direction while degrading antibunching in the opposite direction. This extended nonreciprocal thermal effect, detailed in a recent paper published July 22, 2026, provides a pathway toward directional phonon switches with potential applications in chiral networks and phononic information processing.

Researchers at the School of Physics, Beihang University, in China detailed a scheme leveraging spinning resonators and quadratic optomechanics to achieve this nonreciprocal phonon blockade, published on July 22. The core of the innovation lies in manipulating the Sagnac, Fizeau effect; pump fields traveling in opposite directions experience differing effective detunings, creating an imbalance in intracavity intensities that shifts the mechanical frequency depending on direction. This asymmetry is not simply about blocking phonons, but a sophisticated control where resonance conditions dictate behavior. Analyzing the resulting phonon statistics, the researchers characterized the nonreciprocity using the second-order correlation function, a key metric for quantifying quantum behavior. Unlike typical systems where thermal fluctuations diminish performance, this design benefits from increased thermal noise in a specific direction, reversing the statistics from bunching to antibunching in the opposite direction. This manipulation of phonon statistics, achieved through a combination of spinning resonators and quadratic optomechanical interactions, enables directional phonon switches and chiral networks with potential applications in phononic information processing.

The pursuit of directional control over phonon flow, vibrational energy at the nanoscale, has intensified as researchers seek to build more sophisticated quantum devices. Current approaches typically rely on external magnetic fields or carefully engineered material structures to guide these vibrations, but a new theoretical framework detailed by Yao Dong and Guo-Feng Zhang at the School of Physics, Beihang University, proposes an alternative leveraging the Sagnac, Fizeau effect. Their work, published last month, outlines a system where spinning resonators create asymmetry in light propagation, directly influencing phonon behavior.

Phonon Blockade as a Single-Phonon Source

School of Physics, Beihang University physicists are refining techniques to create highly directional phonon flow, essentially building one-way streets for mechanical vibrations at the nanoscale. Their recent work details a system leveraging spinning resonators to achieve a scheme for generating single phonons, discrete units of vibrational energy, with unprecedented control. This is not simply about stopping phonons, but about manipulating their behavior based on direction. The team’s design utilizes two spinning resonators coupled to a nanomechanical oscillator. This high degree of asymmetry is achieved through the Sagnac, Fizeau effect, where pump fields experience differing effective detunings depending on their propagation direction. This intensity imbalance then shifts the effective mechanical frequency, forming the basis for the directional blockade. The system exhibits a sophisticated interplay between resonance and tunneling, meaning it can either block phonon transmission or allow it via tunneling, depending on the input direction and resonance conditions.

The researchers further analyzed the phonon blockade in terms of interference between the coherent component and squeezed fluctuations, providing insight into the underlying quantum statistics. Incorporating thermal phonons, they reveal an extended nonreciprocal thermal effect, where increasing thermal noise degrades antibunching toward Poissonian statistics in one direction, yet reverses the statistics from bunching to antibunching in the opposite direction.

The ability to precisely control phonon flow holds considerable promise for advancements in phononic information processing and chiral networks. Recent work at the School of Physics, Beihang University, details a method for achieving this control through nonreciprocal phonon blockade. This distinction highlights a key difference between blocking phonons and actively steering them through the system via resonance.

The expectation that stronger driving always improves quantum control is often overturned in advanced optomechanical systems; instead, a newly detailed configuration demonstrates that carefully managing asymmetry is key to achieving pronounced nonlinear effects. This level of nonreciprocity stems from the interplay between the Sagnac, Fizeau effect and optical spring effects within the quadratic optomechanical system.

A contrast ratio exceeding 55 dB demonstrates the pronounced directional control achieved over phonon transmission within a newly designed optomechanical system, effectively establishing a one-way street for mechanical vibrations. Researchers detailed a scheme leveraging spinning resonators to create this asymmetry, a feat previously challenging in quantum acoustic circuits. This high contrast, measured in the phonon second-order correlation function, signifies a substantial preference for phonon propagation in one direction over another.

Researchers at the School of Physics, Beihang University, are actively exploring how to translate their findings on nonreciprocal phonon blockade into functional devices for advanced information processing. These components are crucial for controlling phonon flow, potentially enabling chiral networks where vibrations propagate in a single direction. Beyond simple switching, the ability to manipulate phonon statistics opens possibilities for robust signal transmission. The potential extends to hybrid quantum systems, integrating phonons with superconducting qubits or other quantum platforms. Single-phonon sources, created through phonon blockade, can facilitate quantum frequency conversion and mediate microwave-to-optical quantum transduction, bridging different quantum computing architectures. As the paper notes, these devices could be essential building blocks for future phononic information processing systems, offering a novel approach to quantum communication and computation.