One-Way Entanglement: How Squeezed Magnons Break Reciprocity
11 May 2026, Lynn
Squeezing magnons enables directional entanglement between photons and phonons in a cavity magnomechanics system.
I think it’s safe to say that quantum entanglement is one of the most important phenomena for future technologies. I know it is a quantum effect, but physicists have long had a fascination with making it directional — a one-way link rather than the usual two-way street. Now, a team led by Ziyad Imara at Abdelmalek Essaadi University in Morocco has proposed a way to achieve exactly that: nonreciprocal entanglement among magnons, photons, and phonons, by squeezing the magnon mode.
It turns out that making entanglement flow in only one direction is not just a theoretical curiosity. Imara, together with colleagues Khadija El Anouz, İlkay Demir, and Abderrahim El Allati, has studied this problem in their paper (arXiv:2508.06850). The team proposes “a different theoretical mechanism to achieve nonreciprocal macroscopic entanglement among magnons, photons, and phonons, based on magnon squeezing.” In contrast to earlier work that controlled only frequency shifts, their scheme uses precise control of both the amplitude and phase of a squeezed magnon mode. By flipping the squeezing phase by 180 degrees, they reverse the frequency shift and the effective dissipation rate simultaneously, creating two distinct configurations that allow entanglement to flow in opposite directions.
Inside the Cavity
The system itself is a cavity magnomechanics setup — a device that brings together three very different quantum players. A polished sphere of yttrium iron garnet (YIG), a common magnetic crystal, sits inside a microwave cavity near the region of strongest magnetic field. When a polarizing magnetic field is applied, the spins in the YIG sphere align and can collectively oscillate, forming a magnon mode — a wave of spin excitation. The magnons interact with the microwave photons in the cavity through magnetic dipole coupling, and they also interact with mechanical vibrations (phonons) in the crystal through magnetostrictive forces. This three-way interface makes the system a rich playground for quantum information.
The key twist is the magnon squeezing. Squeezing is a technique borrowed from quantum optics: it reduces the quantum noise in one quadrature of a wave at the expense of increasing noise in the other. For light, squeezing has been used to improve interferometer sensitivity. For magnons, the team applies a similar concept. By driving the YIG sphere with a microwave field at the right frequency, they create a squeezed magnon state. The squeezing is characterized by a parameter (Upsilon) and a phase (theta). By adjusting that phase, the system can be tuned between two regimes: one where the entanglement between magnons and photons is strongly directional while the magnon–phonon entanglement is suppressed in one direction, and another where the roles are reversed.
How Directionality Emerges
The mechanism relies on a subtle interplay. Normally, entanglement between two modes is bidirectional: if mode A is entangled with mode B, then B is entangled with A. But the squeezing introduces an imbalance. When the squeezing phase is set to one value, the magnon mode experiences a frequency shift that makes it preferentially couple to the cavity photons. The magnon–phonon coupling, being magnetostrictive, is left relatively weak. Entanglement flows from the cavity to the magnons but not the other way. When the phase is flipped by 180 degrees, the situation reverses: the magnon–phonon coupling becomes dominant, and entanglement flows from the magnons to the phonons instead.
This is not will on the part of the system — it is a consequence of how squeezing modifies the effective dissipation and coupling rates. The team shows that by choosing the squeezing amplitude appropriately, they can achieve ideal nonreciprocity, where the contrast between forward and reverse entanglement becomes perfect. “We show that the proposed scheme achieves ideal nonreciprocity,” they write, “which can be optimized by cavity-magnon coupling and bath temperature control.”
The bath temperature plays a crucial role. At 10 millikelvin — a temperature routinely achieved in dilution refrigerators — the thermal noise is low enough that the squeezed state remains coherent. The team finds that over a broad temperature range—up to about 240 millikelvin depending on the phase configuration—nonreciprocal entanglement can persist with high contrast. Above that, thermal fluctuations begin to wash out the directional effect.
Why This Matters
Nonreciprocal entanglement is more than a neat trick. In quantum information processing, you often want to isolate certain subsystems while allowing information to flow between others. A one-way entanglement link could be used to protect a quantum memory from back-action: the memory is entangled with a readout mode, but the readout cannot disturb the memory. It could also enable directional quantum communication channels, analogous to optical isolators but at the quantum level.
Moreover, the system the team proposes is within reach of current experimental technology. YIG spheres are well studied, microwave cavities are standard, and magnon squeezing has been demonstrated in recent experiments. The parameters they use — squeezing amplitudes comparable to the cavity decay rate, coupling strengths in the few-megahertz range — are realistic. “This work provides promising perspectives for hybrid magnon-based quantum technologies,” the authors note.
The work is theoretical, not experimental. But the roadmap is clear. Experimental groups working on cavity magnomechanics can now attempt to realize these predictions. The first step would be to demonstrate the two distinct entanglement configurations by varying the squeezing phase. If successful, it would be a proof-of-principle for a new type of quantum control.
There is much more work for Imara and his colleagues to do. They plan to explore how the scheme scales with multiple magnon modes and how it might be integrated into quantum networks. And if the thoroughness of their theoretical analysis is any indication, the approach is ready to be built.
The implications of this work extend beyond the immediate result. For years, researchers have treated entanglement as a symmetric resource. This proposal challenges that assumption, offering a way to make entanglement itself directional. It is a milestone in the ongoing effort to design quantum systems with custom properties. And because the building blocks are already in the lab, the next chapter may be written sooner than expected.
Lynn is an online editor of LoomSci
References
- Ziyad Imara et al., Nonreciprocal Macroscopic Entanglement through Magnon Squeezing in a Cavity Magnomechanics, arXiv:2508.06850