arXiv subjects

M. Buttiker

Publications and source records attributed to M. Buttiker.

At least 19 recordsLinked to original sources

arXiv2012

Optimal pumping of orbital entanglement with single particle emitters

We propose a method for the optimal time-controlled generation of entangled itinerant particles, using on-demand sources in a conductor in the quantum Hall regime. This entanglement pump is realized by applying periodic, tailored voltage pulses to pairs of quantum dots or quantum point contacts. We show that the pump can produce orbital Bell pairs of both electrons and holes at the optimal rate of half a pair per pumping cycle. The entanglement can be detected by a violation of a Bell inequality formulated in terms of low-frequency current cross correlations.

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arXiv2010

Magnetic field induced non-Gaussian fluctuations in macroscopic equilibrium systems

We calculate the magnetic-field dependent nonlinear conductance and noise in a macroscopic inhomogeneous system. If the system does not possess a specific symmetry, the magnetic field induces a nonzero third cumulant of the current even at equilibrium. This cumulant is related to the first and second voltage derivatives of the spectral density and average current in the same way as for mesoscopic quantum-coherent systems. The system provides a robust test of a non-equilibrium fluctuation relation.

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arXiv2010

Dynamics of four- versus two-terminal transport through chaotic quantum cavities

We consider multi-terminal mesoscopic transport through a well-conducting chaotic quantum cavity using random matrix theory. Four-probe resistance vanishes on the average and is not affected by weak localization. Its fluctuations are given by a single expression valid for arbitrary temperature, ac frequency, non-ideal coupling of the contacts, and in the presence of floating probes; surprisingly, they are governed by the dwell time only. In contrast, the two-probe transport additionally depends on the RC-time, which is interpreted as a property of the measurement scheme. We also predict a universal mesoscopic distribution of the phase of transmitted voltage in an ac experiment.

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arXiv2009

Entanglement at finite temperatures in the electronic two-particle interferometer

In this work we discuss a theory for entanglement generation, characterization and detection in fermionic two-particle interferometers at finite temperature. The motivation for our work is provided by the recent experiment by the Heiblum group, Neder et al, Nature 448, 333 (2007), realizing the two particle interferometer proposed by Samuelsson, Sukhorukov, and Buttiker, Phys. Rev. Lett. 92, 026805 (2004). The experiment displayed a clear two-particle Aharonov-Bohm effect, however with an amplitude suppressed due to finite temperature and dephasing. This raised qualitative as well quantitative questions about entanglement production and detection in mesoscopic conductors at finite temperature. As a response to these questions, in our recent work, Samuelsson, Neder, and Buttiker, Phys. Rev. Lett. 102, 106804 (2009) we presented a general theory for finite temperature entanglement in mesoscopic conductors. Applied to the two-particle interferometer we showed that the emitted two-particle state in the experiment was clearly entangled. Moreover, we demonstrated that the entanglement of the reduced two-particle state, reconstructed from measurements of average currents and current cross correlations, constitutes a lower bound to the entanglement of the emitted state. The present work provides an extended and more detailed discussion of these findings.

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arXiv2009

Reduced and projected two-particle entanglement at finite temperatures

We present a theory for two-particle entanglement production and detection in mesoscopic conductors at finite temperature. In contrast to the zero temperature limit, the entanglement of the density matrix projected out of the emitted many-body state is different from the entanglement of the reduced density matrix, detectable by current correlation measurements. We show that under very general conditions the reduced entanglement constitutes a lower bound for the projected entanglement. Applying the theory to the recent experiment [Neder et al, Nature 448 333 (2007)] on a fermionic Hanbury Brown Twiss two-particle interferometer we find that despite an appreciable entanglement production in the experiment, the detectable entanglement is close to zero.

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arXiv2009

Heat production and current noise for single- and double-cavity quantum capacitors

We analyze the frequency-dependent noise and the heat production rate for a dynamical quantum capacitor in the regime in which it emits single particles, electrons and holes. At low temperature and slow driving the relaxation resistance quantum, R_{q} = h/(2e^2), defines the heat production rate in both the linear and non-linear response regimes. If a double-cavity capacitor emits particles in pairs, the noise is enhanced. In contrast the energy dissipated is suppressed or enhanced depending on whether an electron-hole pair or an electron-electron (a hole-hole) pair is emitted.

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arXiv2008

Fluctuation relations without microreversibility in nonlinear transport

In linear transport, the fluctuation-dissipation theorem relates equilibrium current correlations to the linear conductance coefficient. For nonlinear transport, there exist fluctuation relations that rely on Onsager's principle of microscopic reversibility away from equilibrium. However, both theory and experiments have shown deviations from microreversibility in the form of magnetic field asymmetric current-voltage relations. We present novel fluctuation relations for nonlinear transport in the presence of magnetic fields that relate current correlation functions at any order at equilibrium to response coefficients of current cumulants of lower order. We illustrate our results with the example of an electrical Mach-Zehnder interferometer.

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arXiv2008

Cross-correlation of two interacting conductors

We calculate the current cross-correlation for two weakly interacting mesoscopic conductors. Our derivation is based on the two-particle scattering matrix derived in Goorden and Büttiker [Phys. Rev. Lett. {\bf 99}, 146801 (2007)]. We include the Fermi sea in the leads into the theory and show how to calculate transport quantities and specifically cross-correlations. We focus on the zero-frequency current cross-correlation of two chaotic quantum dots and calculate the magnitude of its fluctuations with the help of Random Matrix Theory.

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arXiv2008

Shot noise of a mesoscopic two-particle collider

We investigate the shot noise generated by particle emission from a mesoscopic capacitor into an edge state reflected and transmitted at a quantum point contact (QPC). For a capacitor subject to a periodic voltage the resulting shot noise is proportional to the number of particles (both electrons and holes) emitted during a period. It is proportional to the product of transmission and reflection probability of the QPC independent of the applied voltage but proportional to the driving frequency. If two driven capacitors are coupled to a QPC at different sides then the resulting shot noise is maximally the sum of noises produced by each of the capacitors. However the noise is suppressed depending on the coincidence of the emission of two particles of the same kind.

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arXiv2008

Dynamic scattering channels of a double barrier structure

We calculate analytically the Floquet scattering matrix for a periodically driven double-barrier structure. Our approach takes into account dynamical effects which become necessarily important when electrons propagate through a system subject to a fast drive. It is convenient to represent the Floquet scattering amplitude as a sum of amplitudes corresponding to different times spent by an electron inside the structure. These amplitudes define dynamical scattering channels. Then we represent the dc current generated by the structure as a sum of two generic contributions. The first one is due to photon-assisted interference processes within the same channel and the second one is due to inter-channel interference processes. At zero temperature both contributions are present while at high temperatures and/or high driving frequencies only the former survives.

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arXiv2008

Quantized dynamics of a coherent capacitor

A quantum coherent capacitor subject to large amplitude pulse cycles can be made to emit or reabsorb an electron in each half cycle. Quantized currents with pulse cycles in the GHz range have been demonstrated experimentally. We develop a non-linear dynamical scattering theory for arbitrary pulses to describe the properties of this very fast single electron source. Using our theory we analyze the accuracy of the current quantization and investigate the noise of such a source. Our results are important for future scientific and possible metrological applications of this source.

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arXiv2007

Rectification and nonlinear transport in chaotic dots and rings

We investigate the nonlinear current-voltage characteristic of mesoscopic conductors and the current generated through rectification of an alternating external bias. To leading order in applied voltages both the nonlinear and the rectified current are quadratic. This current response can be described in terms of second order conductance coefficients and for a generic mesoscopic conductor they fluctuate randomly from sample to sample. Due to Coulomb interactions the symmetry of transport under magnetic field inversion is broken in a two-terminal setup. Therefore, we consider both the symmetric and antisymmetric nonlinear conductances separately. We treat interactions self-consistently taking into account nearby gates. The nonlinear current is determined by different combinations of second order conductances depending on the way external voltages are varied away from an equilibrium reference point (bias mode). We discuss the role of the bias mode and circuit asymmetry in recent experiments. In a photovoltaic experiment the alternating perturbations are rectified, and the fluctuations of the nonlinear conductance are shown to decrease with frequency. Their asymptotical behavior strongly depends on the bias mode and in general the antisymmetric conductance is suppressed stronger then the symmetric conductance. We next investigate nonlinear transport and rectification in chaotic rings. To this extent we develop a model which combines a chaotic quantum dot and a ballistic arm to enclose an Aharonov-Bohm flux. In the linear two-probe conductance the phase of the Aharonov-Bohm oscillation is pinned while in nonlinear transport phase rigidity is lost. We discuss the shape of the mesoscopic distribution of the phase and determine the phase fluctuations.

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arXiv2007

Two-particle scattering matrix of two interacting mesoscopic conductors

We consider two quantum coherent conductors interacting weakly via long range Coulomb forces. We describe the interaction in terms of two-particle collisions described by a two-particle scattering matrix. As an example we determine the transmission probability and correlations in a two-particle scattering experiment and find that the results can be expressed in terms of the density-of-states matrices of the non-interacting scatterers.

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arXiv2007

Magnetic-field symmetries of mesoscopic nonlinear conductance

We examine contributions to the dc-current of mesoscopic samples which are non-linear in applied voltage. In the presence of a magnetic field, the current can be decomposed into components which are odd (antisymmetric) and even (symmetric) under flux reversal. For a two-terminal chaotic cavity, these components turn out to be very sensitive to the strength of the Coulomb interaction and the asymmetry of the contact conductances. For both two- and multi-terminal quantum dots we discuss correlations of current non-linearity in voltage measured at different magnetic fields and temperatures.

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arXiv2006

Time-resolved noise of adiabatic quantum pumps

We investigate quantum-statistical correlation properties of a periodically driven mesoscopic scatterer on a time-scale shorter than the period of a drive. In this limit the intrinsic quantum fluctuations in the system of fermions are the main source of a noise. Nevertheless the effect of a slow periodic drive is clearly visible in a two-time current-current correlation function as a specific periodic in time modulation. In the limit of a strong drive such a modulation can change the sign of a current correlation function.

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arXiv2006

Full counting statistics for voltage and dephasing probes

We present a stochastic path integral method to calculate the full counting statistics of conductors with energy conserving dephasing probes and dissipative voltage probes. The approach is explained for the experimentally important case of a Mach-Zehnder interferometer, but is easily generalized to more complicated setups. For all geometries where dephasing may be modeled by a single one-channel dephasing probe we prove that our method yields the same full counting statistics as phase averaging of the cumulant generating function.

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arXiv2006

Parity meter for charge qubits: an efficient quantum entangler

We propose a realization of a charge parity meter based on two double quantum dots alongside a quantum point contact. Such a device is a specific example of the general class of mesoscopic quadratic quantum measurement detectors previously investigated by Mao et al. [Phys. Rev. Lett. 93, 056803 (2004)]. Our setup accomplishes entangled state preparation by a current measurement alone, and allows the qubits to be effectively decoupled by pinching off the parity meter. Two applications of the parity meter are discussed: the measurement of Bell's inequality in charge qubits and the realization of a controlled NOT gate.

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arXiv2005

Multi-particle correlations of an oscillating scatterer

Using multi-particle distribution functions we calculate the correlations produced by a periodically driven scatterer in a system of noninteracting electrons at zero temperature. The multi-particle correlations due to a quantum exchange effect are expressed in terms of photon-assisted scattering amplitudes. The results we obtain are valid for slow but arbitrary in strength driving. We show that even for large amplitude pumps the zero-frequency noise power is related to two-particle correlations. In addition to two-particle correlations a large amplitude pump can generate multi-particle correlations.

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