Dephasing in a Mach-Zehnder Interferometer by an Ohmic Contact

Abstract

We study dephasing in an electronic Mach-Zehnder (MZ) interferometer based on quantum Hall edge states by a micrometer-sized Ohmic contact embedded in one of its arms. We find that at the filling factor ν=1, as well as in the case where an Ohmic contact is connected to a MZ interferometer by a quantum point contact that transmits only one electron channel, the phase coherence may not be fully suppressed. Namely, if the voltage bias Δμ and the temperature T are small compared to the charging energy of the Ohmic contact E_{C}, the free fermion picture is manifested, and the visibility saturates at its maximum value. At large biases, Δμ≫E_{C}, the visibility decays in a power-law manner.

Transmitting the quantum state of electrons across a metallic island with Coulomb interaction

“…2(b)). We observe first that the quantum interferences' visibility remains of the same high amplitude, which corresponds to a perfect fidelity (at experimental accuracy) of the replicated quantum states imprinted on the electrons reemitted from the island, in agreement with low temperature predictions [9,13]. Second, the magnetic field period of 305±4 µT is found to be larger than in the standard MZI configuration of Fig.…”

“…In the floating MZI limit of strongly connected channels Q = eV pl ∆, with ∆ ≃ 1.7 mV the Coulomb diamond period [10][11][12]. A quantum phase shift of 2πQ e therefore applies to the transferred electrons, as specifically predicted theoretically [9,13], and in agreement with Friedel's sum rule. Comparing with the device set in the standard MZI configuration, we show in Fig.…”

“…However, independent absorption and emission of electrons result in fluctuations of the total island charge Q, with a characteristic charging energy E C = e 2 2C (with C the geometrical capacitance of the island and e the elementary electron charge). At low temperatures T ≪ E C k B (with k B the Boltzmann constant) this energy is not available, and the macroscopic quantum charge state Q is effectively frozen [8,9] (although not quantized in units of e as long as one channel is perfectly connected [10][11][12]). Consequently, correlations develop between absorbed and emitted elec- * These authors contributed equally to this work.…”

“…Another consequence is that heat evacuation from the island's internal states along the channel is fully suppressed [8]. In contrast, in the presence of two or more open channels the coherence is lost [9], and heat evacuation is restored in agreement with the recently observed systematic heat Coulomb blockade of one ballistic channel [14]. Interestingly, the 'electron teleportation' proposed in [5] also relies on the 'all-important' Coulomb charging energy of a small island, although combined in that case with Majorana bound states in an altogether different mechanism.…”

Nonlinear phase estimation: Parity measurement approaches the quantum Cramér-Rao bound for coherent states

“…As the super-resolution criterion, the full width at half maximum (FWHM) of the main peak gets narrow when increasing mean photon number, i.e., the signal's super-resolved characteristic becomes more obvious. Moreover, the signal possesses a 100% visibility [44,45], in that the minimum sits at 0. The definition of visibility refers to In addition, the signal takes on the value of 1 for ϕ = 0, this means that the parity is always even in port B.…”