Electronic Interferometer Research Articles

Counting statistics and dephasing transition in an electronic Mach-Zehnder interferometer

It was recently suggested that a novel type of phase transition may occur in the visibility of electronic Mach-Zehnder Interferometers. Here, we present experimental evidence for the existence of this transition. The transition is induced by strongly non-Gaussian noise that originates from the strong coupling of a quantum point contact to the interferometer. We provide a transparent physical picture of the effect, by exploiting a close analogy to the neutrino-oscillations of particle physics. In addition, our experiment constitutes a probe of the singularity of the elusive full counting statistics of a quantum point contact.

Quantum heat engines based on electronic Mach-Zehnder interferometers

We theoretically investigate the thermoelectric properties of heat engines based on Mach-Zehnder interferometers. The energy dependence of the transmission amplitudes in such setups arises from a difference in the interferometer arm lengths. Any thermoelectric response is thus of purely quantum mechanical origin. In addition to an experimentally established three-terminal setup, we also consider a two-terminal geometry as well as a four-terminal setup consisting of two interferometers. We find that Mach-Zehnder interferometers can be used as powerful and efficient heat engines which perform well under realistic conditions.

Coupling of drumhead vibrations: Experimental and numerical analysis

Many musical drums, such as snare drums, bass drums, and tom toms, consist of two stretched membranes at opposite ends of a cylindrical shell. Vibrations of the two heads are coupled acoustically by the enclosed air and mechanically by the shell itself. The degree of coupling varies with modal frequency and shape, and depends on several factors including the geometry of the drum shell (diameter and length) and the tensions of the two heads. Experimental measurements of coupled vibrations on drums of various sizes have been made using an electronic speckle-pattern interferometer to image the deflection shapes, amplitudes, and relative phases of both heads simultaneously. These measurements are compared with a finite element model of the system that illuminates the role of the vibrational patterns of the enclosed air in the coupling process.

The a.c. Josephson effect without superconductivity.

Superconductivity derives its most salient features from the coherence of the associated macroscopic wave function. The related physical phenomena have now moved from exotic subjects to fundamental building blocks for quantum circuits such as qubits or single photonic modes. Here we predict that the a.c. Josephson effect—which transforms a d.c. voltage Vb into an oscillating signal cos (2eVbt/ħ)—has a mesoscopic counterpart in normal conductors. We show that when a d.c. voltage Vb is applied to an electronic interferometer, there exists a universal transient regime where the current oscillates at frequency eVb/h. This effect is not limited by a superconducting gap and could, in principle, be used to produce tunable a.c. signals in the elusive 0.1–10-THz ‘terahertz gap’.

Scanning gate microscopy of quantum contacts under parallel magnetic field: Beating patterns between spin-split transmission peaks or channel openings

We study the conductance $g$ of an electron interferometer created in a two dimensional electron gas between a nanostructured contact and the depletion region induced by the charged tip of a scanning gate microscope. Using non-interacting models, we study the beating pattern of interference fringes exhibited by the images giving $g$ as a function of the tip position when a parallel magnetic field is applied. The analytical solution of a simplified model allows us to distinguish between two cases: (i) If the field is applied everywhere, the beating of Fabry-P\'erot oscillations of opposite spins gives rise to interference rings which can be observed at low temperatures when the contact is open between spin-split transmission resonances. (ii) If the field acts only upon the contact, the interference rings cannot be observed at low temperatures, but only at temperatures of the order of the Zeeman energy. For a contact made of two sites in series, a model often used for describing an inversion-symmetric double-dot setup, a pseudo-spin degeneracy is broken by the inter-dot coupling and a similar beating effect can be observed without magnetic field at temperatures of the order of the interdot coupling. Eventually, numerical studies of a quantum point contact with quantized conductance plateaus confirm that a parallel magnetic field applied everywhere or only upon the contact gives rises to similar beating effects between spin-split channel openings.

Axial loading verification method for small bones using carrier fringes in speckle pattern interferometry

A computerized system for real-time displacement visualization using carrier fringes in an electronic speckle in-plane sensitive interferometer allows force calibration for micro-displacement analysis of rat bones and verification of axial loading conditions. Once the force has been calibrated and the load is applied along the bone axis, the difference-of-phase method is used to obtain the phase map, which after phase unwrapping, allows the evaluation of the displacements produced by the bone deformation. The proposed method avoids common loading mistakes using first carrier fringes to assure that the loads are within the measuring capabilities of the in-plane interferometer and the Carré phase-stepping method to compensate for linear phase step miscalibration. The experimental results obtained with the calibration of loading forces and axial loading verification show the advantages of the system proposed here over a system which uses a cantilever configuration to make a similar bone deformation analysis.

Probing theν=52quantum Hall state with electronic Mach-Zehnder interferometry

It was recently pointed out that Halperin's 113 topological order explains the transport experiments in the quantum Hall liquid at filling factor $\nu=5/2$. The 113 order, however, cannot be easily distinguished from other likely topological orders at $\nu=5/2$ such as the non-Abelian Pfaffian and anti-Pfaffian states and the Abelian Halperin 331 state in Fabry-Perot interferometry. We show that an electronic Mach-Zehnder interferometer provides a clear identification of these candidate $\nu=5/2$ states. Specifically, the $I$-$V$ curve for the tunneling current through the interferometer is more asymmetric in the 113 state than in other $\nu=5/2$ states. Moreover, the Fano factor for the shot noise in the interferometer can reach 13.6 in the 113 state, much greater than the maximum Fano factors of 3.2 in the Pfaffian and anti-Pfaffian states and 2.3 in the 331 state.

Quantum tomography of an electron.

The complete knowledge of a quantum state allows the prediction of the probability of all possible measurement outcomes, a crucial step in quantum mechanics. It can be provided by tomographic methods which have been applied to atomic, molecular, spin and photonic states. For optical or microwave photons, standard tomography is obtained by mixing the unknown state with a large-amplitude coherent photon field. However, for fermions such as electrons in condensed matter, this approach is not applicable because fermionic fields are limited to small amplitudes (at most one particle per state), and so far no determination of an electron wavefunction has been made. Recent proposals involving quantum conductors suggest that the wavefunction can be obtained by measuring the time-dependent current of electronic wave interferometers or the current noise of electronic Hanbury-Brown/Twiss interferometers. Here we show that such measurements are possible despite the extreme noise sensitivity required, and present the reconstructed wavefunction quasi-probability, or Wigner distribution function, of single electrons injected into a ballistic conductor. Many identical electrons are prepared in well-controlled quantum states called levitons by repeatedly applying Lorentzian voltage pulses to a contact on the conductor. After passing through an electron beam splitter, the levitons are mixed with a weak-amplitude fermionic field formed by a coherent superposition of electron-hole pairs generated by a small alternating current with a frequency that is a multiple of the voltage pulse frequency. Antibunching of the electrons and holes with the levitons at the beam splitter changes the leviton partition statistics, and the noise variations provide the energy density matrix elements of the levitons. This demonstration of quantum tomography makes the developing field of electron quantum optics with ballistic conductors a new test-bed for quantum information with fermions. These results may find direct application in probing the entanglement of electron flying quantum bits, electron decoherence and electron interactions. They could also be applied to cold fermionic (or spin-1/2) atoms.

On-demand maximally entangled states with a parity meter and continuous feedback

Generating on-demand maximally entangled states is one of the cornerstones for quantum information processing. Parity measurements can serve to create Bell states and have been implemented via an electronic Mach-Zehnder interferometer among others. However, the entanglement generation is necessarily harmed by measurement-induced dephasing processes in one of the two parity subspaces. In this work, we propose two different schemes of continuous feedback for a parity measurement. They enable us to avoid both the measurement-induced dephasing process and the experimentally unavoidable dephasing, e.g., due to fluctuations of the gate voltages controlling the initialization of the qubits. We show that we can generate maximally entangled steady states in both parity subspaces. Importantly, the measurement scheme we propose is valid for implementation of parity measurements with feedback loops in various solid-state environments.

Decoherence in a double-dot Aharonov-Bohm interferometer: Numerical renormalization group study

Coherence in electronic interferometers is typically believed to be restored fully in the limit of small voltages, frequencies, and temperatures. However, it is crucial to check this essentially perturbative argument by nonperturbative methods. Here we use the numerical renormalization group to study ac transport and decoherence in an experimentally realizable model interferometer, a parallel double quantum dot coupled to a phonon mode. The model allows us to clearly distinguish renormalization effects from decoherence. We discuss finite-frequency transport and confirm the restoration of coherence in the dc limit.

Current Partition at Topological Channel Intersections

An intersection between one-dimensional chiral channels functions as a topological current splitter. We find that the splitting of a chiral zero-line mode obeys very simple yet highly counterintuitive partition laws that relate current paths to the geometry of the intersection. Our results have far reaching implications for electron beam splitter and interferometer device proposals based on chiral transport, and for understanding transport in systems in which multiple topological domains lead to a statistical network of chiral channels.

Dynamical control of interference using voltage pulses in the quantum regime.

As a general trend, nanoelectronics experiments are shifting towards frequencies so high that they become comparable to the device's internal characteristic time scales, resulting in new opportunities for studying the dynamical aspects of quantum mechanics. Here we theoretically study how a voltage pulse (in the quantum regime) propagates through an electronic interferometer (Fabry-Perot or Mach-Zehnder). We show that extremely fast pulses provide a conceptually new tool for manipulating quantum information: the possibility to dynamically engineer the interference pattern of a quantum system. Striking physical signatures are associated with this new regime: restoration of the interference in presence of large bias voltages; negative currents with respect to the direction of propagation of the voltage pulse; and oscillation of the total transmitted charge with the total number of injected electrons. The present findings have been made possible by the recent unlocking of our capability for simulating time-resolved quantum nanoelectronics of large systems.

Wave-function description of conductance mapping for a quantum Hall electron interferometer

Scanning gate microscopy of quantum point contacts (QPC) in the integer quantum Hall regime is considered in terms of the scattering wave functions with a finite-difference implementation of the quantum transmitting boundary approach. Conductance ($G$) maps for a clean QPC as well as for a system including an antidot within the QPC constriction are evaluated. The steplike locally flat $G$ maps for clean QPCs turn into circular resonances that are reentrant in an external magnetic field when the antidot is introduced to the constriction. The current circulation around the antidot and the spacing of the resonances at the magnetic field scale react to the probe approaching the QPC. The calculated $G$ maps with a rigid but soft antidot potential reproduce the features detected recently in the electron interferometer [F. Martins et al., Sci. Rep. 3, 1416 (2013)].

Theoretical, numerical, and experimental study of a flying qubit electronic interferometer

We discuss an electronic interferometer recently measured by Yamamoto et al. This "flying quantum bit" experiment showed quantum oscillations between electronic trajectories of two tunnel-coupled wires connected via an Aharanov-Bohm ring. We present a simple scattering model as well as a numerical microscopic model to describe this experiment. In addition, we present new experimental data to which we confront our numerical results. While our analytical model provides basic concepts for designing the flying qubit device, we find that our numerical simulations allow to reproduce detailed features of the transport measurements such as in-phase and anti-phase oscillations of the two output currents as well as a smooth phase shift when sweeping a side gate. Furthermore, we find remarkable resemblance for the magneto conductance oscillations in both conductance and visibility between simulations and experiments within a specific parameter range.

Correction of dephasing oscillations in matter-wave interferometry

Vibrations, electromagnetic oscillations and temperature drifts are among the main reasons for dephasing in matter-wave interferometry. Sophisticated interferometry experiments, e.g. with ions or heavy molecules, often require integration times of several minutes due to the low source intensity or the high velocity selection. Here we present a scheme to suppress the influence of such dephasing mechanisms - especially in the low-frequency regime - by analyzing temporal and spatial particle correlations available in modern detectors. Such correlations can reveal interference properties that would otherwise be washed out due to dephasing by external oscillating signals. The method is shown experimentally in a biprism electron interferometer where a perturbing oscillation is artificially introduced by a periodically varying magnetic field. We provide a full theoretical description of the particle correlations where the perturbing frequency and amplitude can be revealed from the disturbed interferogram. The original spatial fringe pattern without the perturbation can thereby be restored. The technique can be applied to lower the general noise requirements in matter-wave interferometers. It allows for the optimization of electromagnetic shielding and decreases the efforts for vibrational or temperature stabilization.

레이저 간섭계를 이용한 배관 용접부 잔류응력 평가

용접 잔류응력은 용접공정에서 발생하는 하는데, 용접 구조물의 결함 유발 및 파괴의 주요 원인이 된다. 본 논문에서는 전자 처리 레이저 스페클 간섭법을 이용하여 원전 배관의 용접부 잔류응력을 측정하였다. 인장시험기를 이용하여 용접된 배관에 압축 하중을 가하였으며, 면내 변형 측정 간섭계를 이용하여 용접부와 모재부의 변형을 측정하였고, 제안된 수식에 의하여 탄성계수를 측정하였다. 용접 배관에 가해지는 하중에 따라 변형이 일정하게 증가하며, 용접 배관의 모재부와 용접부에 발생한 변형을 비교하였을 때, 모재부의 변형이 더 크게 나타남을 확인할 수 있었다. 용접 배관 모재부의 탄성계수는 202.46 GPa, 용접부의 탄성 계수는 212.14 GPa, 잔류응력은 6.29 MPa로 측정되었다. Residual stresses that occur during the welding process, are the main cause of failure and defects in welded structures. This paper, presents the use of an electronic processing laser speckle interferometer to measure the residual stress of a welded pipe for a nuclear power plant. A tensile testing machine was used to evaluate a welded pipe that failed in compression. The inform plane deformation and modulus of elasticity of the base metal and welds were measured using an interferometer. Varying the load on the welded pipe had a larger effect on the deformation of the base metal the other properties of the base metal and welds. The elastic moduli of the base metal and weld of the welded pipe were 202.46 and 212.14 GPa, respectively, the residual stress was measured to be 6.29 MPa.

An electron Talbot-Lau interferometer and magnetic field sensing

We present a demonstration of a three grating Talbot-Lau interferometer for electrons. As a proof of principle, the interferometer is used to measure magnetic fields. The device is similar to the classical Moiré deflectometer. The possibility to extend this work to build a scaled-up electron deflectometer or interferometer for sensitive magnetic field sensing is discussed.

Postselective measurement of the electronic entanglement in the system of two Mach-Zehnder interferometers with coulomb interaction

The parameters at which the maximally entangled two-particle state appears in the system of two ideal electronic Mach-Zehnder interferometers are known. In this work, the operation of nonideal devices with finite scattering in splitters and with reflection in the region of the Coulomb Interaction has been considered. It has been shown that, under the condition of postselection of experimental results, these factors can increase the observed Bell parameter to values exceeding Cirel’son’s (or Tsirelson’s) bound equal to 2√2 up to the mathematical limit equal to 4. A simple postselective measurement scheme providing B = 4 has been described. Although the results of such measurements are not as fundamental as the observation of the violation of Bell’s inequality, they can indirectly indicate the existence of an entangled state in the system. The measurement system is more stable against fluctuations of the phase than a system without postselection. Furthermore, it has been found that the proposed system is optimal for investigation of cross correlations between interferometers in the dc regime (beyond the paradigm of the violation of Bell’s inequality) because they cannot be generated by coordinated fluctuations of Aharonov-Bohm phases.

Measurements of coupled drumhead vibrations using electronic speckle-pattern interferometry

Many musical drums such as snare drums, tom toms, and bass drums consist of two membranes at opposite ends of a cylindrical shell. Striking one head causes both to vibrate, as their motions are coupled due to the enclosed air as well as the shell itself. An optical system consisting of two electronic speckle-pattern interferometers was constructed allowing operating deflection shapes of both heads to be viewed simultaneously while the drum is driven acoustically at a resonant frequency. This system allows the determination of the relative phases, orientations, and amplitudes of the vibrational patterns on the two heads. Previously reported results for coupled drumheads were verified and extended to include the effects of degenerate single membrane mode pairs that are split due to non-uniform tension in the heads. Examples of higher frequency coupled patterns are also shown. Parameters influencing the degree of coupling are described briefly and compared qualitatively with results from a finite element model.

Transport phenomena in helical edge state interferometers: A Green's function approach

We analyze the current and the shot-noise of an electron interferometer made of the helical edge states of a two-dimensional topological insulator within the framework of non-equilibrium Green's functions formalism. We study in detail setups with a single and with two quantum point contacts inducing scattering between the different edge states. We consider processes preserving the spin as well as the effect of spin-flip scattering. In the case of a single quantum point contact, a simple test based on the shot-noise measurement is proposed to quantify the strength of the spin-flip scattering. In the case of two single point contacts with the additional ingredient of gate voltages applied within a finite-size region at the top and bottom edges of the sample, we identify two type of interference processes in the behavior of the currents and the noise. One of such processes is analogous to that taking place in a Fabry-P\'erot interferometer, while the second one corresponds to a configuration similar to a Mach-Zehnder interferometer. In the helical interferometer these two processes compete.