Remote nonreciprocal magnon magnon entanglement via the Barnett effect with coherent feedback

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The gist

The gist: A scheme for generating and controlling remote nonreciprocal magnon–magnon entanglement in a cavity magnonic system with coherent feedback was proposed using two microwave cavities driven

In short

The study proposes a method to create and control remote nonreciprocal entanglement between magnons in two separated microwave cavities using coherent feedback and squeezed vacuum inputs. By exploiting the Barnett effect, reversing the bias magnetic field direction switches this entanglement on or off, allowing for complete nonreciprocity. The scheme offers tunable parameters for precise control over these quantum correlations.

Key concepts

Barnett Effect
This effect describes how reversing the direction of a static magnetic field changes the frequency of a rotating YIG sphere. In this system, this change in magnon frequency is used to introduce nonreciprocity, meaning the physical outcome depends on whether the bias field is applied in one direction or the opposite.
Nonreciprocal Entanglement
This refers to quantum correlations between magnons that are different when the physical setup (like the magnetic field direction) is reversed. The scheme achieves this by using the Barnett effect; entanglement exists for one magnetic field orientation but disappears for the other, demonstrating a directional dependence in quantum correlation.
Coherent Feedback
This involves sending a portion of the cavity's output back into it to influence its behavior. In this context, coherent feedback is used to enhance the magnon-magnon entanglement at an optimal level when tuned correctly, providing a mechanism for controlling the strength of the quantum correlation.
Squeezed Vacuum Fields
These are specialized microwave fields that have reduced noise in one quadrature (like amplitude or phase) at the expense of increased noise in another. Using independent single-mode squeezed vacuum fields drives the two cavities, and their relative squeezing phases offer an additional layer of control over how quantum correlations are transferred.

Terminology used across episodes

This episode discusses

The paper

Remote nonreciprocal magnon magnon entanglement via the Barnett effect with coherent feedback · Read on arXiv

School of Physics and Astronomy, Beijing Normal University

Transcript

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Today's paper: "Remote nonreciprocal magnon magnon entanglement via the Barnett effect with coherent feedback".

Mira: The gist:

Kai: First, who's behind it and why it matters.

Paper summary: Kai: So looking at "Remote nonreciprocal magnon magnon entanglement via the Barnett effect with coherent feedback," what does this paper really tell us about building these kinds of systems? It seems like they've laid out a path to getting controllable remote quantum correlations in cavity magnonic setups >

Mira: They’re demonstrating how the combination of the Barnett effect, cavity detuning, and feedback can allow you to switch that entanglement on or off depending on the direction of the magnetic field you apply >

Lev: From an error correction angle, I think this control over nonreciprocity is crucial because if you can flip it like that, it opens up possibilities for more robust quantum protocols >

Kai: It shows a controllable approach to preparing these kinds of nonreciprocal quantum correlations in cavity magnonic systems >

Mira: The paper really highlights the interplay between the input squeezing and the feedback loop as the primary control mechanisms for these remote connections >

Conclusion: Kai: So we’re wrapping up on this paper about remote nonreciprocal magnon entanglement, titled "Remote nonreciprocal magnon magnon entanglement via the Barnett effect with coherent feedback."

Mira: It basically shows how you can link two separate microwave cavities together, using a spinning magnetic material in one cavity and a stationary one in the other to create correlations between their spin excitations.

Lev: The authors are talking about using that Barnett effect—basically reversing the bias field changes the direction of entanglement—and they're controlling it with feedback and detuning settings.

Kai: So, what does this actually mean for us? It means we can build a system where you can decide which way the quantum information flows between two distant points in a chip or even across a lab setup.

Mira: They are showing that you get complete nonreciprocity by tuning the detuning and feedback phase so that entanglement only exists in one magnetic field direction and vanishes for the other.

Lev: From an error correction standpoint, that control is significant because it gives you a switch to turn those correlations on or off precisely when needed.

Kai: The numbers they’re throwing around show how coherent feedback boosts the entanglement at a certain level of reflectivity, but if you push the feedback too hard, it actually reduces the amount.

Mira: And they also found that using unequal squeezing factors for the input fields helps improve entanglement even when you keep the total number of photons in both cavities fixed.

Lev: That's interesting because it suggests we don't just need perfect symmetry in our input states to get good results in this setup.

Kai: So, to sum up, they’ve given us a controllable recipe for creating these remote quantum links using cavity magnonics and the Barnett effect.

Mira: It really moves the discussion past just getting entanglement and into how you can precisely engineer its directionality and robustness.

Lev: We’re going to look at some of those specific control parameters next, like how much feedback is actually needed to make this work reliably in a real device.

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