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Aephraim M. Steinberg

Publications and source records attributed to Aephraim M. Steinberg.

At least 19 recordsLinked to original sources
arXiv2026

Matter wave bistability with a momentum chirped Bose-Einstein condensate

While a Fabry-Perot (FP) cavity interferometer is a standard tool in modern optics, analogous physics can also be observed with matter waves such as Bose-Einstein condensates (BECs). Interatomic collisions in BECs can induce nonlinear features such as multi-valued transmission spectra for interferometry experiments. Observation of interaction effects in the matter-wave analogue of FP interferometry has not yet been experimentally achieved, mostly due to broadening of transmission peaks by interaction-induced shifts of cavity resonances. In this work, we theoretically show that this limitation can be overcome by engineering a momentum chirp in a BEC wavepacket. By balancing this chirp against the dynamical mean-field energy shift of the cavity during transmission, we predict enhanced resonant spectra and bistability features due to interaction-assisted tunneling that would be otherwise inaccessible. We show that this physics is readily observable with quasi-one-dimensional BECs of cold atoms colliding with a pair of light-induced Gaussian potential barriers forming the cavity. We also benchmark the requisite optimum chirp needed and characterize the contrast of near-discontinuous FP transmission spectra at an interacting resonance. Our findings enable the realization of technologies like matter-wave switching protocols, and high-precision velocity measurements; estimates of achievable sensitivity for the latter are provided.

cond-mat.quant-gas↗
arXiv2026

Measuring the spin of a spin-1/2 and getting a result of 7

The weak value of an operator is the average result of measuring that operator on a quantum system given specified initial and final states. The overlap between these states appears in the denominator of the weak value, and thus if that overlap is small, the weak value can be arbitrarily large. In 1988, Albert, Aharonov, and Vaidman proposed a weak Stern-Gerlach experiment which would be able to measure a so-called anomalous weak value, a measurement result which lies out- side of the eigenvalue spectrum of the operator being measured. Though anomalous weak values have been measured in numerous optical systems, here we present the first such realization of this experiment as originally proposed. By placing a Bose-Einstein condensate of 87Rb in a magnetic gradient and performing an unlikely postselection, we measure an effective magnification of a weak magnetic momentum kick (~ 8 $μ$m/s) by a factor of 14. We also demonstrate that increasing the momentum kick decreases the "weakness" of the measurement and reduces the amplification.

quant-ph↗
arXiv2026

Sub-Rayleigh Imaging of Unequal-Intensity Sources: Near-Quantum-Limit Multiparameter Estimation

In optical imaging, diffraction strongly degrades the performance of conventional intensity-based estimation once the separation between two sources is below the Rayleigh-Abbe limit. Recent developments showed that this limitation can be surpassed using spatial-mode demultiplexing (SPADE), and this was demonstrated in several experiments for two equal-intensity spots of unknown separation. When there are multiple unknown parameters, as in the case of several unequal sources with unknown intensities and unknown separation, cross-talk among the parameters makes the multi-parameter estimation problem significantly more challenging. In this paper, we adapt super-resolved position localization by inversion of coherence along an edge (SPLICE) to estimate both the separation and relative intensity of two incoherent sources simultaneously. We demonstrate a clear advantage over direct imaging (DI), achieving a root mean squared error (RMSE) approximately $50 \%$ larger than the quantum limit and a sixfold improvement over DI within the range of parameters we tested. This improvement can be even greater for smaller separations and larger intensity imbalances when crosstalk is suppressed.

physics.optics↗
arXiv2026

Spin coherence scale: operator-ordering sensitivity beyond the Heisenberg-Weyl group

We introduce the spin coherence scale as a measure of quantum coherence for spin systems, generalizing the quadrature coherence scale (QCS) previously defined for quadrature observables. This SU($2$)-invariant measure quantifies the off-diagonal coherences of a quantum state in angular momentum bases, weighted by the classical distinguishability of the superposed states. It serves as a witness of nonclassicality, provides both upper and lower bounds on the Hilbert-Schmidt distance to the set of classical (spin coherent) states, and bounds the Wigner negativity of a spin state. We demonstrate that many hallmark properties of the QCS carry over to the spin setting, including its links to noise susceptibility of a state and moments of quasiprobability distributions and its experimental realizability with a two-copy scheme. The spin coherence scale has direct implications for quantum metrology in the guise of rotation sensing. We also generalize the framework to SU($n$) systems, identifying the unique SU($n$)-invariant depolarization channel and outlining a broad, Lie-algebraic approach to defining and characterizing the properties of coherence scale beyond harmonic oscillators.

quant-ph↗
arXiv2026

Improved delta-kick cooling with multiple nonideal kicks

Delta-kick cooling is a technique employed to achieve low kinetic temperatures by decreasing momentum width at the cost of increased position width. In an ideal implementation, this method uses a harmonic potential to deliver a single near-instantaneous momentum kick. In practice, potentials that are approximately harmonic near their center are commonly used. As a result, the breakdown of the harmonic approximation far from the center limits the cooling performance. Inspired by aberration cancellation in optics, we propose to use compound matter-wave lens systems for $δ-$kick cooling with Gaussian potentials. By strategically combining attractive and repulsive kicks, we show that it is possible to mimic the effect of a harmonic potential. For a test case with reasonable experimental parameters, our method suggests a reduction in kinetic temperature by a factor of $2.5$ using a 2-pulse sequence and by a factor of $3.2$ using a 3-pulse sequence.

quant-ph↗
arXiv2026

Information gain and measurement disturbance for quantum agents

The traditional formalism of quantum measurement (hereafter ``TQM'') describes processes where some properties of quantum states are extracted and stored as classical information. While TQM is a natural and appropriate description of how humans interact with quantum systems, it is silent on the question of how a more general, quantum, agent would do so. How do we describe the observation of a system by an observer with the ability to store not only classical information but quantum states in its memory? In this paper, we extend the idea of measurement to a more general class of sensors for quantum agents which interact with a system in such a way that the agent's memory stores information (classical or quantum) about the system under study. For appropriate sensory interactions, the quantum agent may ``learn'' more about the system than would be possible under any set of classical measurements -- but as we show, this comes at the cost of additional measurement disturbance. We experimentally demonstrate such a system and characterize the tradeoffs by considering the channel capacity required to erase the effect of a measurement.

quant-ph↗
arXiv2026

Compressing Quantum Fisher Information

We show that the quantum Fisher information about any phase parameter encoded in a family of pure quantum states can be faithfully compressed into a single qubit, accompanied by a logarithmic amount of classical bits. When the phase is encoded into many identical copies of a qubit state on the equator of the Bloch sphere, we show that the compression can be implemented sequentially, by iteratively compressing pairs of qubits into a single qubit. We experimentally demonstrate this building block in a photonic setup, developing two alternative compression strategies, based on Type-I fusion gate and a postselected implementation of the CNOT gate.

quant-ph↗
arXiv2026

Theory of direct measurement of the quantum pseudo-distribution via its characteristic function

We propose a method for directly measuring the quantum mechanical pseudo-distribution of observable properties via its characteristic function. Vandermonde matrices of the eigenvalues play a central role in the theory. This proposal directly finds the pseudo-distribution using weak measurements of the generator of position moments (momentum translations). While the pseudo-distribution can be extracted from the data in a theory-agnostic way, it is shown that under quantum-mechanical formalism, the predicted pseudo-distribution is identified with the Kirkwood-Dirac pseudo-distribution. We discuss the construction of both the joint pseudo-distribution and a conditional pseudo-distribution, which is closely connected to weak-value physics. By permuting position and momentum measurements, we give a prescription to directly probe the canonical commutation relation and verify it for any quantum state. This work establishes the theory of a characteristic function approach to pseudo-distributions, as well as providing a constructive approach to measuring them directly.

quant-ph↗
arXiv2024

Experimental evidence that a photon can spend a negative amount of time in an atom cloud

When a pulse of light traverses a material, it incurs a time delay referred to as the group delay. Should the group delay experienced by photons be attributed to the time they spend as atomic excitations? However reasonable this connection may seem, it appears problematic when the frequency of the light is close to the atomic resonance, as the group delay becomes negative in this regime. To address this question, we use the cross-Kerr effect to probe the degree of atomic excitation caused by a resonant transmitted photon, by measuring the phase shift on a separate beam that is weak and off-resonant. Our results, over a range of pulse durations and optical depths, are consistent with the recent theoretical prediction that the mean atomic excitation time caused by a transmitted photon (as measured via the time integral of the observed phase shift) equals the group delay experienced by the light. Specifically, we measure mean atomic excitation times ranging from $(-0.82\pm 0.31) τ_0$ for the most narrowband pulse to $(0.54\pm 0.28) τ_0$ for the most broadband pulse, where $τ_0$ is the non-post-selected excitation time, given by the scattering (absorption) probability multiplied by the atomic lifetime $τ_{\rm sp}$. These results suggest that negative values taken by times such as the group delay have more physical significance than has generally been appreciated.

quant-ph↗
arXiv2024

Variable-strength non-local measurements reveal quantum violations of classical counting principles

We implement a variant of the quantum pigeonhole paradox thought experiment to study whether classical counting principles survive in the quantum domain. We observe strong measurements significantly violate the pigeonhole principle (that among three pigeons in two holes, at least one pair must be in the same hole) and the sum rule (that the number of pigeon pairs in the same hole is the sum of the number of pairs across each of the holes) in an ensemble that is pre and postselected into particular separable states. To investigate whether measurement disturbance is a viable explanation for these counter-intuitive phenomena, we employ the first ever variable-strength measurement of a non-local observable. As we decrease the measurement strength, we find the violation of the sum rule decreases, yet the pigeonhole principle remains violated. In the weak limit, the sum rule is restored due to the cancellation between two weak values with equal and opposite imaginary parts. We observe the same kind of cancellation at higher measurement strengths, thus raising the question: do strong measurements have imaginary parts?

quant-ph↗
arXiv2024

Do qubits dream of entangled sheep? Quantum measurement without classical output

Quantum mechanics is usually formulated with an implicit assumption that agents who can observe and interact with the world are external to it and have a classical memory. However, there is no accepted way to define the quantum-classical cut and no a priori reason to rule out fully quantum agents with coherent quantum memories. In this work, we introduce an entirely quantum notion of measurement, called a sensation, to account for quantum agents that experience the world through quantum sensors. Sensations eschew probabilities and instead describe a deterministic flow of quantum information. We quantify the information gain and disturbance of a sensation using concepts from quantum information theory and find that sensations always disturb at least as much as they inform. Viewing measurements as sensations could lead to a new understanding of quantum theory in general and to new results in the context of quantum networks.

quant-ph↗
arXiv2023

Generating a 4-photon Tetrahedron State: Towards Simultaneous Super-sensitivity to Non-commuting Rotations

It is often thought that the super-sensitivity of a quantum state to an observable comes at the cost of a decreased sensitivity to other non-commuting observables. For example, a squeezed state squeezed in position quadrature is super-sensitive to position displacements, but very insensitive to momentum displacements. This misconception was cleared with the introduction of the compass state, a quantum state equally super-sensitive to displacements in position and momentum. When looking at quantum states used to measure spin rotations, N00N states are known to be more advantageous than classical methods as long as they are aligned to the rotation axis. When considering the estimation of a rotation with unknown direction and amplitude, a certain class of states stands out with interesting properties. These states are equally sensitive to rotations around any axis, are second-order unpolarized, and can possess the rotational properties of platonic solids in particular dimensions. Importantly, these states are optimal for simultaneously estimating the three parameters describing a rotation. In the asymptotic limit, estimating all d parameters describing a transformation simultaneously rather than sequentially can lead to a reduction of the appropriately-weighted sum of the measured parameters' variances by a factor of d. We report the experimental creation and characterization of the lowest-dimensional such state, which we call the "tetrahedron state" due to its tetrahedral symmetry. This tetrahedron state is created in the symmetric subspace of four optical photons' polarization in a single spatial and temporal mode, which behaves as a spin-2 particle. While imperfections due to the hardware limit the performance of our method, we argue that better technology can improve our method to the point of outperforming any other existing strategy in per-photon comparisons.

quant-ph↗
arXiv2023

How much time does a photon spend as an atomic excitation before being transmitted?

When a single photon traverses a cloud of 2-level atoms, the average time it spends as an atomic excitation -- as measured by weakly probing the atoms -- can be shown to be the spontaneous lifetime of the atoms multiplied by the probability of the photon being scattered into a side mode. A tempting inference from this is that an average scattered photon spends one spontaneous lifetime as an atomic excitation, while photons that are transmitted spend zero time as atomic excitations. However, recent experimental work by some of us [PRX Quantum 3, 010314 (2022)] refutes this intuition. We examine this problem using the weak-value formalism and show that the time a transmitted photon spends as an atomic excitation is equal to the group delay, which can take on positive or negative values. We also determine the corresponding time for scattered photons and find that it is equal to the time delay of the scattered photon pulse, which consists of a group delay and a time delay associated with elastic scattering, known as the Wigner time delay. This work provides new insight into the complex and surprising histories of photons travelling through absorptive media.

quant-ph↗
arXiv2023

Experimental Communication Through Superposition of Quantum Channels

Information capacity enhancement through the coherent control of channels has attracted much attention of late, with work exploring the effect of coherent control of channel causal orders, channel superpositions, and information encoding. Coherently controlling channels necessitates a non-trivial expansion of the channel description, which for superposing qubit channels, is equivalent to expanding the channel to act on qutrits. Here we explore the nature of this capacity enhancement for the superposition of channels by comparing the maximum coherent information through depolarizing qubit channels and relevant superposed and qutrit channels. We show that the expanded qutrit channel description in itself is sufficient to explain the capacity enhancement without any use of superposition.

quant-ph↗
arXiv2023

Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and Spin-independent Interactions

We observe spin rotations caused by atomic collisions in a non-equilibrium Bose-condensed gas of $^{87}$Rb. Reflection from a pseudomagnetic barrier creates counterflow in which forward- and backward-propagating matter waves have partly transverse spin directions. Even though inter-atomic interaction strengths are state-independent, the indistinguishability of parallel spins leads to spin dynamics. A local magnetodynamic model, which captures the salient features of the observed spin textures, highlights an essential connection between four-wave mixing and collisional spin rotation. The observed phenomenon has previously been thought to exist only in nondegenerate gases; our observations and model clarify the nature of these effective-magnetic spin rotations.

cond-mat.quant-gas↗
arXiv2023

Beyond transcoherent states: Field states for effecting optimal coherent rotations on single or multiple qubits

Semiclassically, laser pulses can be used to implement arbitrary transformations on atomic systems; quantum mechanically, residual atom-field entanglement spoils this promise. Transcoherent states are field states that fix this problem in the fully quantized regime by generating perfect coherence in an atom initially in its ground or excited state. We extend this fully quantized paradigm in four directions: First, we introduce field states that transform an atom from its ground or excited state to any point on the Bloch sphere without residual atom-field entanglement. The best strong pulses for carrying out rotations by angle $θ$ are are squeezed in photon-number variance by a factor of $\rm{sinc}θ$. Next, we investigate implementing rotation gates, showing that the optimal Gaussian field state for enacting a $θ$ pulse on an atom in an arbitrary, unknown initial state is number squeezed by less: $\rm{sinc}\tfracθ{2}$. Third, we extend these investigations to fields interacting with multiple atoms simultaneously, discovering once again that number squeezing by $\tfracπ{2}$ is optimal for enacting $\tfracπ{2}$ pulses on all of the atoms simultaneously, with small corrections on the order of the ratio of the number of atoms to the average number of photons. Finally, we find field states that best perform arbitrary rotations by $θ$ through nonlinear interactions involving $m$-photon absorption, where the same optimal squeezing factor is found to be $\rm{sinc}θ$. Backaction in a wide variety of atom-field interactions can thus be mitigated by squeezing the control fields by optimal amounts.

quant-ph↗
arXiv2023

Obtaining a Single-Photon Weak Value from Experiments using a Strong (Many-Photon) Coherent State

A common type of weak-value experiment prepares a single particle in one state, weakly measures the occupation number of another state, and post-selects on finding the particle in a third state (a 'click'). Most weak-value experiments have been done with photons, but the heralded preparation of a single photon is difficult and slow of rate. Here we show that the weak value mentioned above can be measured using strong (many-photon) coherent states, while still needing only a 'click' detector such as an avalanche photodiode. One simply subtracts the no-click weak value from the click weak-value, and scales the answer by a simple function of the click probability.

quant-ph↗
arXiv2022

Efficient Adiabatic Rapid Passage in the Presence of Noise

Adiabatic Rapid Passage (ARP) is a powerful technique for efficient transfer of population between quantum states. In the lab, the efficiency of ARP is often limited by noise on either the energies of the states or the frequency of the driving field. We study ARP in the simple setting of a two-level system subject to sinusoidal fluctuations on the energy level separation by numerically solving the optical Bloch equations in the absence of damping. We investigate the dependence of the efficiency of population transfer on the frequency and amplitude of the perturbation, and find that it is predominantly affected by resonant coupling when the detuning matches the frequency of the noise. We present intuitive principles for when ARP becomes inefficient within this model, and provide a sufficient condition for the population transfer to be above an arbitrary threshold.

quant-ph↗