Optical Propulsion and Levitation of Metajets

Kaushik Kudtarkar; Preston Cunha; Sam Lin; Shoufeng Lan; Xinyi Wang; Yixin Chen; Yongmin Liu; Zi Jing Wong; Ziqiang Cai

arxiv: 2502.17334 · v1 · submitted 2025-02-24 · ⚛️ physics.optics

Optical Propulsion and Levitation of Metajets

Kaushik Kudtarkar , Yixin Chen , Ziqiang Cai , Preston Cunha , Xinyi Wang , Sam Lin , Zi Jing Wong , Yongmin Liu

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Shoufeng Lan

This is my paper

Pith reviewed 2026-05-23 02:11 UTC · model grok-4.3

classification ⚛️ physics.optics

keywords metajetsoptical forceslevitationpropulsionmetasurfacessilicon nanopillarsphase gradientlight sails

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The pith

Metajets achieve three-dimensional optical propulsion and levitation through meta-atom phase gradients.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops a first-principles theory of optical forces from refraction and reflection and shows that metajets, objects built from metasurfaces, can be driven in three dimensions when an extra wavevector component is supplied. This is accomplished by arranging silicon nanopillars to impose a spatially varying phase gradient across the structure. Experiments and simulations confirm both in-plane propulsion and out-of-plane levitation that increase with incident power and do not depend on object size. A reader would care because the approach suggests optical manipulation of objects at scales far larger than current traps allow.

Core claim

By creating a spatially distributed phase gradient with deliberately arranged silicon nanopillars, an extra wavevector component is introduced that enables three-dimensional motions of metajets through optical forces generated by refraction and reflection at an interface, with experiments and simulations confirming in-plane propulsion and out-of-plane levitation that align with the theory.

What carries the argument

Spatially distributed phase gradient created by silicon nanopillars that supplies the additional wavevector component needed for three-dimensional optical forces on metajets.

If this is right

Metaphotonic force magnitude increases with incident light power.
The force remains effective regardless of metajet size.
The same mechanism can be applied to large-scale objects such as interstellar light sails.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Phase-gradient designs could be transferred to other metasurface geometries to produce controlled translation or rotation at macroscopic distances.
Power scaling without size limit suggests the possibility of combining many metajets into larger steerable structures.
The approach may complement existing optical-trapping methods when extended to vacuum or low-pressure environments.

Load-bearing premise

The deliberately arranged nanopillars produce a phase gradient whose extra wavevector dominates over scattering losses or mechanical constraints.

What would settle it

Removal or randomization of the nanopillar phase gradient while keeping total power and average refractive index fixed, followed by direct observation that levitation and directed propulsion both disappear.

read the original abstract

The quintessential hallmark distinguishing metasurfaces from traditional optical components is the engineering of subwavelength meta-atoms to manipulate light at will. Enabling this freedom, in a reverse manner, to control objects constituted by metasurfaces could expand our capability of optical manipulation to go beyond the predominant microscopic and sub-microscopic scales. Here, we introduce a driving metaphotonic force fully controllable by meta-atoms to manipulate structured objects named metajets. Upon Newton's law of motion that can apply to classical and relativistic mechanics, we develop a first-principles theory to analyze optical forces generated by refraction and reflection at an interface. We find that three-dimensional motions of metajets would be possible if one could introduce an extra wavevector component. We achieve that by creating a spatially distributed phase gradient with deliberately arranged silicon nanopillars. Our experiments and simulations reveal an in-plane propulsion and, very importantly, out-of-plane levitation of the metajets, aligning well with the theory. We also find that the metaphotonic force augments with increased light power but is not limited by the size of metajets, which could unleash new opportunities for metaphotonic control in large settings, such as interstellar light sails.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Metajets achieve experimental 3D optical motion via nanopillar phase gradients, but the force derivation leaves scattering losses unaddressed in the given details.

read the letter

The paper's core result is experimental in-plane propulsion plus out-of-plane levitation of these metajets, produced by a spatially varying phase gradient from arranged silicon nanopillars. The authors derive the forces from basic refraction and reflection at an interface using Newton's laws, then add an extra wavevector component to enable the vertical motion. Experiments and simulations line up with that picture, and the force scales with power without an obvious size limit. That last point is useful if the goal is larger-scale optical control such as light sails. The framing as a reverse use of metasurface meta-atoms is straightforward and the first-principles starting point avoids unnecessary fitting parameters. Credit for showing the levitation is real in the lab setup. The main gap is whether scattering from the nanopillars was folded into the force calculation or bounded in the data. At visible or near-IR wavelengths those pillars scatter, so unaccounted momentum loss into scattered fields could mimic or mask the intended mechanism. The abstract claims good alignment but supplies no error bars, fit residuals, or explicit loss terms, which makes it difficult to judge how cleanly the intended metaphotonic force explains the levitation. A reader working on optical manipulation or metasurface devices would find the concept worth seeing, even if the quantitative support needs more work. Groups thinking about light sails might pick up the size-independent scaling idea. The paper is coherent enough on its own terms to merit referee time rather than a desk reject; reviewers can press on the loss accounting and data selection without the work falling apart first.

Referee Report

2 major / 0 minor

Summary. The manuscript introduces metajets as metasurface-structured objects and develops a first-principles theory based on Newton's laws to analyze optical forces generated by refraction and reflection at an interface. It shows that three-dimensional motions, including out-of-plane levitation, become possible by introducing an extra wavevector component via a spatially distributed phase gradient engineered with silicon nanopillars. Experiments and simulations are reported to demonstrate in-plane propulsion and out-of-plane levitation that align with the theory; the metaphotonic force is found to increase with light power and to be independent of metajet size.

Significance. If the central claims hold, the work would be significant for expanding optical manipulation beyond microscopic scales. The demonstration of controllable, size-independent forces enabling levitation via metasurface phase gradients could open pathways for macroscopic applications such as light sails. The first-principles derivation from Newton's laws and the reported consistency across theory, simulation, and experiment represent strengths that would advance metaphotonics if rigorously supported by quantitative evidence.

major comments (2)

[Theory] Theory section (as summarized in the abstract): The first-principles analysis of optical forces from refraction and reflection, derived from Newton's laws, does not include or bound momentum dissipation into scattered fields from the silicon nanopillars. This omission is load-bearing for the claim that the phase gradient supplies a net out-of-plane force for levitation, since scattering losses at visible/near-IR wavelengths could dominate or alter the force balance.
[Results] Results (abstract): The claim that experiments and simulations 'align well with the theory' for in-plane propulsion and out-of-plane levitation lacks quantitative support such as error bars, data selection criteria, or fit statistics. Without these, it is not possible to verify whether the observed levitation is attributable to the intended metaphotonic mechanism rather than unmodeled effects.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed review. The comments identify important areas for strengthening the manuscript, and we address each point below with plans for revision.

read point-by-point responses

Referee: [Theory] Theory section (as summarized in the abstract): The first-principles analysis of optical forces from refraction and reflection, derived from Newton's laws, does not include or bound momentum dissipation into scattered fields from the silicon nanopillars. This omission is load-bearing for the claim that the phase gradient supplies a net out-of-plane force for levitation, since scattering losses at visible/near-IR wavelengths could dominate or alter the force balance.

Authors: We agree that bounding scattering is necessary for rigor. Our derivation applies Newton's laws to the net momentum transfer at the engineered interface, where the spatially distributed phase gradient from the nanopillars imparts the additional wavevector component. However, to directly address the referee's concern, we will revise the Theory section to include an explicit bound on momentum carried away by scattered fields. This will be done by estimating the scattered power fraction using the nanopillar geometry and operating wavelength, supported by supplementary FDTD calculations showing that scattering remains a minor contribution relative to the designed refraction/reflection forces. The revised analysis will confirm that the phase-gradient term still provides the dominant out-of-plane component. revision: yes
Referee: [Results] Results (abstract): The claim that experiments and simulations 'align well with the theory' for in-plane propulsion and out-of-plane levitation lacks quantitative support such as error bars, data selection criteria, or fit statistics. Without these, it is not possible to verify whether the observed levitation is attributable to the intended metaphotonic mechanism rather than unmodeled effects.

Authors: We accept that quantitative metrics are required to substantiate the agreement. In the revised manuscript we will expand the Results section to report error bars on all propulsion and levitation data (from repeated trials), explicit data-selection criteria (including number of samples and outlier handling), and statistical measures such as R-squared values or residual analysis for the match between theory, simulation, and experiment. These additions will allow direct assessment of whether the observed motions are consistent with the metaphotonic force model. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation is self-contained first-principles analysis

full rationale

The paper states it develops a first-principles theory from Newton's laws applied to refraction and reflection forces at an interface, deriving the requirement for an extra wavevector component to enable 3D metajet motion. This condition is then implemented via a phase gradient from arranged silicon nanopillars, with experiments and simulations serving as independent validation that aligns with the derived predictions. No equations reduce to fitted inputs by construction, no load-bearing self-citations are invoked, and no ansatz or uniqueness claims are smuggled in; the central result rests on the interface force analysis and external experimental test rather than tautological renaming or parameter fitting.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 2 invented entities

The central claim rests on standard physical laws plus newly introduced concepts; no free parameters are mentioned in the abstract.

axioms (1)

domain assumption Newton's law of motion applies to metajets under both classical and relativistic mechanics
Explicitly invoked as the foundation for developing the first-principles theory of optical forces.

invented entities (2)

metajets no independent evidence
purpose: Structured objects constituted by metasurfaces whose motion is controlled by meta-atoms
New class of objects introduced to extend optical manipulation beyond microscopic scales.
metaphotonic force no independent evidence
purpose: Driving force fully controllable by meta-atoms for manipulating metajets
Newly named force arising from engineered phase gradients.

pith-pipeline@v0.9.0 · 5763 in / 1216 out tokens · 65272 ms · 2026-05-23T02:11:27.122053+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

1 extracted references · 1 canonical work pages

[1]

1 Feynman, R. P. & Hibbs, A. R. Quantum Mechanics and Path Integrals . (McGraw-Hill, 1965). 2 McInnes, C. R. Solar Sailing: Technology, Dynamics and Mission Applications. (Springer, 1999). 3 Magnusson, R. & Gaylord, T. K. Diffraction efficiencies of thin phase gratings with arbitrary grating shape. J. Opt. Soc. Am. 68, 806-809 (1978). 4 Bomzon, Z., Biener...

work page 1965

[1] [1]

1 Feynman, R. P. & Hibbs, A. R. Quantum Mechanics and Path Integrals . (McGraw-Hill, 1965). 2 McInnes, C. R. Solar Sailing: Technology, Dynamics and Mission Applications. (Springer, 1999). 3 Magnusson, R. & Gaylord, T. K. Diffraction efficiencies of thin phase gratings with arbitrary grating shape. J. Opt. Soc. Am. 68, 806-809 (1978). 4 Bomzon, Z., Biener...

work page 1965