arXiv subjects

Eyal Buks

Publications and source records attributed to Eyal Buks.

At least 19 recordsLinked to original sources

arXiv2026

Disentanglement in the macroscopic limit

The recently proposed spontaneous disentanglement hypothesis is formulated using a modified Schrödinger equation having an added nonlinear term. The hypothesis is motivated by some outstanding issues in the foundations of quantum mechanics, including the problem of quantum measurement. Spontaneous disentanglement is explored in the current study for the macroscopic limit. This is done using some many--body models having known exact solutions. For the under--study models, it is found that non--local entanglement becomes unstable in the macroscopic limit. On the other hand, stability in the macroscopic limit of local entanglement is not excluded. These findings demonstrate that the spontaneous disentanglement hypothesis can bridge between the quantumness of the microscopic realm, and the classicalness of the macroscopic one.

quant-ph↗

arXiv2026

The spontaneous disentanglement hypothesis and causality

The hypothesis that disentanglement spontaneously occurs in quantum systems is motivated by some outstanding issues in the foundations of quantum mechanics. However, for some cases, spontaneous disentanglement enables the violation of the causality principle. To mitigate the conflict with causality, a formulation for the hypothesis, which is based on the maximum entropy principle, is proposed. The method of Lagrange multipliers is implemented to ensure consistency with causality. The proposed formulation is applicable for any quantum system having a Hilbert space of finite dimensionality.

quant-ph↗

arXiv2026

Disentanglement by deranking and by suppression of correlation

The spontaneous disentanglement hypothesis is motivated by some outstanding issues in standard quantum mechanics, including the problem of quantum measurement. The current study compares between some possible methods that can be used to implement the hypothesis. Disentanglement is formulated using a nonlinear operator, which can be used to modify both the Schrödinger equation for the quantum state vector, and the master equation for the density operator. Two types of nonlinear disentanglement operators are explored. The first one gives rise to matrix deranking, and the second one to correlation suppression. Both types are demonstrated using a two spin system that is driven close to the Hartmann--Hahn double resonance. It is shown that limit cycle steady state solutions, which are excluded by standard quantum mechanics, become possible in the presence of disentanglement.

quant-ph↗

arXiv2025

Parametric excitation of a ferrimagnetic sphere resonator

The response of a ferrimagnetic sphere resonator to an externally applied parametric excitation is experimentally studied. Measurement results are compared with predictions derived from a theoretical model, which is based on the hypothesis that disentanglement spontaneously occurs in quantum systems. According to this hypothesis, time evolution is governed by a modified master equation having an added nonlinear term that deterministically generates disentanglement. It is found that the disentanglement--based model is compatible with the experimental results. In particular, the model can qualitatively account for an experimentally observed instability in the system under study, which cannot be derived from any theoretical model that is based on a linear master equation.

quant-ph↗

arXiv2025

A fiber-loop laser with a cooled erbium-doped section

An optical comb featuring an unusual structure has been recently observed in a fiber-loop laser running at cryogenic temperatures. In the present work, the effect of optical polarization on the operation of the laser is explored. Multi--mode lasing with a relatively high degree of inter--mode coherency is experimentally demonstrated. The setup can be used for applications to spectroscopy, communications, and quantum data storage.

physics.optics↗

arXiv2025

Sideband Spectroscopy in the Strong Driving Regime: Volcano Transparency and Sideband Anomaly

We study the response of a spin to two crossed magnetic fields: a strong and fast transverse field, and a weak and slow longitudinal field. We characterize the sideband response at the sum and the difference of driving frequencies over a broad range of parameters. In the strong transverse driving regime, the emission spectrum has a characteristic volcano lineshape with a narrow central transparency region surrounded by asymmetric peaks. Next, we couple the spin to a nonlinear cavity that both drives and measures it. In a sufficiently slow longitudinal field, the emission spectrum exhibits anomalous behavior, where the resonances in both the right and left sidebands lie on the same side of the central resonance. The theoretical results are compared to the experimental measurement of the emission of substitutional nitrogen P1 and nitrogen-vacancy NV$^-$ defects in diamond.

cond-mat.other↗

arXiv2025

Disentanglement-induced superconductivity

The current study is motivated by a difficulty to reconcile between particle number conservation and superconductivity. An alternative modeling, which is based on the hypothesis that disentanglement spontaneously ocuurs in quantum systems, is explored. The Fermi-Hubbard mode is employed to demonstrate a disentanglement-induced quantum phase transition into a state having a finite superconducting order parameter. Moreover, the effect of disentanglement on Josephson junction's current phase relation is explored.

quant-ph↗

arXiv2025

Disentanglement--induced bistability in a magnetic resonator

Multi--stability in the response of a ferrimagnetic spin resonator to an externally applied driving is experimentally studied. The observed multi--stability cannot be derived from any master equation that linearly depends on the spins' reduced density operator. Traditionally, the nonlinearity that is required in order to theoretically account for the observed multi--stability is introduced by implementing the method of Bosonization. Here, an alternative explanation, which is based on the hypothesis that disentanglement spontaneously occurs in quantum systems is explored. According to this hypothesis, time evolution is governed by a master equation having an added nonlinear term, which deterministically generates disentanglement. Experimental results are compared with predictions derived from both competing theoretical models. It is found that better agreement with data is obtained from the disentanglement--based model. This finding, together with a difficulty to justify the Bosonization--based model, indirectly support the spontaneous disentanglement hypothesis.

quant-ph↗

arXiv2024

Spontaneous disentanglement of indistinguishable particles

A master equation containing a nonlinear term that gives rise to disentanglement has been recently investigated. In this study, a modified version, which is applicable for indistinguishable particles, is proposed, and explored for both the Bose-Hubbard and the Fermi-Hubbard models. It is found for both Bosons and Fermions that disentanglement can give rise to quantum phase transitions.

quant-ph↗

arXiv2024

Disentanglement-induced multistability

Multistability cannot be derived from any theoretical model that is based on a monostable master equation. On the other hand, multistability is experimentally-observed in a variety of quantum systems. A master equation having a nonlinear term that gives rise to disentanglement has been recently proposed . The dynamics governed by this master equation is explored for a quantum system made of coupled spins. It is found that the added nonlinear term can give rise to multistability. The spins' response to an externally applied magnetic field is evaluated, and both a phase transition and a dynamical instability are found. These findings, which originate from disentanglement-induced multistability, indirectly support the hypothesis that spontaneous disentanglement occurs in quantum systems.

quant-ph↗

arXiv2024

Polarimeter optical spectrum analyzer

A coherent optical spectrum analyzer is integrated with a rotating quarter wave plate polarimeter. The combined polarimeter optical spectrum analyzer (POSA) allows the extraction of the state of polarization with high spectral resolution. POSA is used in this work to study two optical systems. The first is an optical modulator based on a ferrimagnetic sphere resonator. POSA is employed to explore the underlying magneto-optical mechanism responsible for modulation sideband asymmetry. The second system under study is a cryogenic fiber loop laser, which produces an unequally spaced optical comb. Polarization measurements provide insights on the nonlinear processes responsible for comb creation. Characterizations extracted from POSA data provide guidelines for performance optimization of applications based on these systems under study.

physics.optics↗

arXiv2024

Spontaneous disentanglement and thermalisation

The problem of quantum measurement can be partially resolved by incorporating a process of spontaneous disentanglement into quantum dynamics. We propose a modified master equation, which contains a nonlinear term giving rise to both spontaneous disentanglement and thermalisation. We find that the added nonlinear term enables limit cycle steady states, which are prohibited in standard quantum mechanics. This finding suggests that an experimental observation of such a limit cycle steady state can provide an important evidence supporting the spontaneous disentanglement hypothesis.

quant-ph↗

arXiv2023

Intermode coupling in a fiber loop laser at low temperatures

We experimentally study an unequally-spaced optical comb (USOC), which is generated by a unidirectional fiber loop laser operated at low temperatures. The underlying mechanism responsible for USOC formation is explored using both close and open loop measurements. The role played by dispersion is investigated using radio frequency spectrum measurements. By integrating a saturable absorber into the loop, a lasing state is revealed, in which mode locking coexists with the USOC.

physics.optics↗

arXiv2023

Frequency mixing spectroscopy of spins in diamond

Frequency mixing processes in spin systems have a variety of applications in meteorology and in quantum data processing. Spin spectroscopy based on frequency mixing offers some advantages, including the ability to eliminate crosstalk between driving and detection. We experimentally explore nonlinear frequency mixing processes with negatively charged nitrogen-vacancy defects in diamond at low temperatures, and near level anti crossing. The experimental setup allows simultaneously applying magnetic driving in the longitudinal and transverse directions. Magnetic resonance detection is demonstrated using both Landau Zener Stückelberg interferometry and two-tone driving spectroscopy. The experimental results are compared with predictions of a theoretical analysis based on the rotating wave approximation.

quant-ph↗

arXiv2023

Partial disentanglement in a multipartite system

We explore a nonlinear extension to quantum theory giving rise to deterministic partial disentanglement between pairs of particles. The extension is based on a modified Schrödinger equation having an added nonlinear term. To avoid conflicts with the principles of causality and separability, it is postulated that disentanglement is active only during the time when particles interact. A butterfly-like effect is found near highly entangled multipartite vector states.

quant-ph↗

arXiv2023

Spontaneous collapse by entanglement suppression

We study a recently proposed modified Schrödinger equation having an added nonlinear term, which gives rise to disentanglement. The process of quantum measurement is explored for the case of a pair of coupled spins. We find that the deterministic time evolution generated by the modified Schrödinger equation mimics the process of wavefunction collapse. Added noise gives rise to stochasticity in the measurement process. Conflict with both principles of causality and separability can be avoided by postulating that the nonlinear term is active only during the time when subsystems interact. Moreover, in the absence of entanglement, all predictions of standard quantum mechanics are unaffected by the added nonlinear term.

quant-ph↗

arXiv2023

Tunable multimode lasing in a fiber ring

We experimentally study a fiber loop laser with an integrated Erbium doped fiber (EDF). The output optical spectrum is measured as a function of the EDF temperature. We find that below a critical temperature of about 10K the measured optical spectrum exhibits a sequence of narrow and unequally-spaced peaks. Externally injected light and filtering are employed for tuning the peaks' wavelengths. Operation of the device as an optical memory having storage time of about 20 ms is demonstrated. The multimode lasing tunability can be exploited for novel applications in the fields of sensing, communication, and quantum data storage.

physics.optics↗

arXiv2023

High temperature spectroscopy of nitrogen vacancy centers in diamond

We study spectroscopy of negatively charged nitrogen-vacancy center in diamond at high temperatures under high vacuum conditions. Spin resonances are studied using optical detection of magnetic resonance (ODMR), and optical spectroscopy is employed to study radiative transitions. Upon increasing the temperature the intensity of radiative decay in visible and infra-red decreased. In addition, the ODMR resonance frequencies were decreased, and the phonon line emission shifted to higher wavelengths. Fitting the measured intensity of photo-luminescence with the theoretical predictions of the Mott-Seitz model yields the value of $0.24 \operatorname{eV}$ for the energy barrier associated with nonradiative decay.

quant-ph↗