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Parity detection and entanglement with a Mach-Zehnder interferometer
A parity meter projects the state of two qubits onto two subspaces with
different parities, the states in each parity class being indistinguishable. It
has application in quantum information for its entanglement properties. In our
work we consider the electronic Mach-Zehnder interferometer (MZI) coupled
capacitively to two double quantum dots (DQDs), one on each arm of the MZI.
These charge qubits couple linearly to the charge in the arms of the MZI. A key
advantage of an MZI is that the qubits are well separated in distance so that
mutual interaction between them is avoided. Assuming equal coupling between
both DQDs and the arms and the same bias for each DQD, this setup usually
detects three different currents, one for the odd states and two for each even
state. Controlling the magnetic flux of the MZI, we can operate the MZI as a
parity meter: only two currents are measured at the output, one for each parity
class. In this configuration, the MZI acts as an ideal detector, its Heisenberg
efficiency being maximal. For a class of initial states, the initially
unentangled DQDs become entangled through the parity measurement process with
probability one.Comment: 9 pages, 2 figure
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Room-Temperature Power-Stabilized Narrow-Linewidth Tunable Erbium-Doped Fiber Ring Laser Based on Cascaded Mach-Zehnder Interferometers with Different Free Spectral Range for Strain Sensing
An automatically power-stabilized (with power fluctuation <0.155 dB), narrow-linewidth (0.0171 nm), wavelength-tunable (10.69 nm) erbium-doped fiber laser has been proposed by cascading two fiber Mach-Zehnder interferometers (MZI) without using any temperature controlling device. One of the MZIs (here called the 1st MZI) is composed of two 3 dB couplers to form interference patterns while the other MZI (here termed the 2nd MZI) is constructed with a tapered seven-core fiber (SCF) and based on the principle of supermode interference. For the two MZIs, the free spectral range (FSR), the passband bandwidth and the extinction ratio (ER) at 1560 nm are 0.37 nm, 0.19 nm, 16.6 dB and 13.93 nm, 7.93 nm, 10.1 dB, respectively. Due to the major difference between the two FSR values, the 1st MZI and the 2nd MZI respectively play a role in controlling the laser linewidth and suppressing the homogeneous broadening effect to reach to a satisfactory level of power stability. The 2nd MZI is also used to fine tune the laser wavelength by applying strain to the tapered SCF (TSCF) over the spectral range of 1570.22-1559.33 nm, with an incremental step of 0.37 nm being used. The side-mode suppression ratio (SMSR) of the tunable fiber laser can be up to 45 dB. By appropriately adjusting the polarization controller, dual wavelength lasing can also be achieved. For single wavelength lasing, the 3 dB laser linewidth is 0.0171 nm. The power fluctuation, without a temperature controlling device being used and operating at room temperature, is found to be less than 0.155 dB over 1 hour while the central wavelength drift is less than 0.19 nm
Spatial coherence effects on second- and fourth-order temporal interference
We report the results of two experiments performed with two-photon light,
produced via collinear degenerate optical spontaneous parametric downconversion
(SPDC), in which both second-order (one-photon) and fourth-order (two-photon)
interferograms are recorded in a Mach-Zehnder interferometer (MZI). In the
first experiment, high-visibility fringes are obtained for both the second- and
fourth-order interferograms. In the second experiment, the MZI is modified by
the removal of a mirror from one of its arms; this leaves the fourth-order
interferogram unchanged, but extinguishes the second-order interferogram. A
theoretical model that takes into consideration both the temporal and spatial
degrees-of-freedom of the two-photon state successfully explains the results.
While the temporal interference in the MZI is independent of the spatial
coherence of the source, that of the modified MZI is not
Investigating transfer of learning in advanced quantum mechanics
Research suggests that students often have difficulty transferring their
learning from one context to another. We examine upper-level undergraduate and
graduate students' facility with questions about the interference pattern in
the double-slit experiment (DSE) with single photons and polarizers of various
orientations placed in front of one or both slits. Before answering these types
of questions, students had worked through a tutorial on the Mach-Zehnder
Interferometer (MZI) in which they learned about interference of single photons
when polarizers of various orientations are placed in the two paths of the MZI.
After working on the MZI tutorial, students were asked similar questions in the
isomorphic context of the DSE. We discuss the extent to which they were able to
transfer what they learned in the context of the MZI to analogous problems in
the isomorphic context of the DSE.Comment: 4 pages, 3 figure
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