<i>In situ</i> control of electron gas dimensionality in freely suspended semiconductor membranes

Höhberger, Eva M.; Krämer, Tomas; Wegscheider, Werner; Blick, Robert H.

doi:10.1063/1.1580641

Cited by 19 publications

(24 citation statements)

References 15 publications

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“…This has been discussed e.g. in connection with quantum dots: in order to reduce the electron-phonon interaction the acoustic mode spectra have been modified by suspended phonon cavities [4] and control of electron dephasing in an electron-phonon cavity has been proposed [5]. Phonon cavities allow for coherent coupling of discrete electronic states with discrete phonon states [6], in resemblance to cavity QED [7].…”

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confidence: 99%

Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers

Elser

Marquardt

Glöckl

et al. 2007

2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference

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Guided Acoustic Wave Brillouin Scattering (GAWBS) generates phase and polarization noise of light propagating in glass fibers. This excess noise affects the performance of various experiments operating at the quantum noise limit. We experimentally demonstrate the reduction of GAWBS noise in a photonic crystal fiber in a broad frequency range using cavity sound dynamics. We compare the noise spectrum to the one of a standard fiber and observe a 10-fold noise reduction in the frequency range up to 200 MHz. Based on our measurement results as well as on numerical simulations we establish a model for the reduction of GAWBS noise in photonic crystal fibers.PACS numbers: 42.50.-p, 42.81.-i The impact of thermally excited acoustic phonon modes is a severe hindrance for the performance of a variety of physical systems. In gravitational wave detection, for example, the thermal excitation of internal acoustic modes of the interferometer mirrors is a limiting factor to the measurement sensitivity [1], in solid state quantum dots electron-phonon interactions lead to decoherence [2], and also in fiber optics the detrimental character of acoustic phonon modes has been encountered [3]. A general strategy to reduce the amplitude of phonon modes is to cool the environment to extremely low temperatures. This technique is however very inconvenient, in particular when employed to fibers connecting distant points. Another possibility is making use of cavity sound dynamics and modifying the phonon spectrum by tailoring the boundary conditions for sound waves through spatial structuring. This has been discussed e.g. in connection with quantum dots: in order to reduce the electron-phonon interaction the acoustic mode spectra have been modified by suspended phonon cavities [4] and control of electron dephasing in an electron-phonon cavity has been proposed [5]. Phonon cavities allow for coherent coupling of discrete electronic states with discrete phonon states [6], in resemblance to cavity QED [7]. The possibility to completely suppress phonon scattering of excitons by combining different effects, one of them being the fabrication of smaller structures, has been pointed out in [8]. Sound attenuation and phononic band-gaps have been studied theoretically and experimentally in one-[9], two-[10] and three-[11] dimensional periodic structures. Sonic band-gaps in a preform of a photonic crystal fiber (PCF) [12] have been calculated and measured in [13]. Light-sound interactions can on the other hand be deliberately enhanced by structuring the environment of the phonons, e.g. in a double-cavity being simultaneously resonant for photons and phonons [14]. Recently, confinement of acoustic modes in the core of a photonic crystal fiber has been demonstrated [15].In this Letter we suggest and experimentally demonstrate a convenient method to reduce acoustic modes in optical fibers: by using an appropriately tailored photonic crystal fiber we find that the impact of acoustic vibrations in comparison to a standard fiber can be reduced owing to t...

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confidence: 99%

Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers

Elser

Marquardt

Glöckl

et al. 2007

2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference

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“…Unlike bulk material, the confined structure supports the tailoring of the phonon density of states by altering the dimensions. [18][19][20][21] Therefore, the charge qubit in a confined structure is expected to exhibit some interesting characteristics.…”

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confidence: 99%

“…With advances in novel nanofabrication technology, quantum dots can now be embedded into the suspended structure. 20,21 Most of the structure is spatially separated from most of the substrate such that the acoustic modes between the surfaces can be ideally and completely confined. The in-plane scale is assumed to exceed substantially the width and dot size.…”

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confidence: 99%

Decoherence of a charge qubit embedded inside a suspended phonon cavity

et al. 2008

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This study elucidates the theory of phonon-induced decoherence of a double dot charge qubit that is embedded inside a suspended semiconductor slab. The influences of the lattice temperature, width of the slab, and positions of the dots on the decoherence are analyzed. Numerical results indicate that the decoherence in the slab system is weaker than that in a bulk environment. In particular, the decoherence is markedly suppressed by the inhibition of the electron-phonon coupling. Such a system with low decoherence may be useful for manipulating the qubits.Various candidates for building blocks of quantum computers have been proposed 1-4 and demonstrated 5-8 using nanoscale solid state structures. Among them, the semiconductor double quantum dot ͑DQD͒ is a prototype of a solid state qubit, which comprises a pair of quantum dots connected through an interdot tunneling barrier. 9 The DQD acts as a two-level system when at most one excess electron is allowed in the double dot potential. 10 The two logical states correspond to the localized states of the excess electron in one or the other dot. Accordingly, the state of the charge qubit can be expressed as a linear superposition of the two localized states, and has recently been demonstrated in a GaAs/ AlGaAs heterostructure. 6,7 An important advantage of this system is that all of the qubit parameters can be controlled by varying the external gate voltages. Furthermore, it may have great potential for scalability and integration with current microelectronic technologies.However, various mechanisms may destroy the coherence of the system since the charge qubit can never be isolated completely from its environment. 6 The electron-phonon interaction is one possible decoherence channel and has been theoretically investigated. It ranges from a single charge qubit 11-16 to two coupled charge qubits. 17 Although many works have focused on bulk cases, the decoherence of a charge qubit in a confined structure has received little attention. Unlike bulk material, the confined structure supports the tailoring of the phonon density of states by altering the dimensions. 18-21 Therefore, the charge qubit in a confined structure is expected to exhibit some interesting characteristics.This work investigates the decoherence of a DQD qubit that is embedded inside a suspended semiconductor slab. To study the decoherence of the qubit, the master equation is solved under the Born-Markov approximation. 22-24 The qubit of higher quality is found in the slab system. In particular, the decoherence is dramatically suppressed by the inhibition of the electron-phonon coupling, suggesting that a robust DQD qubit can be achieved in a suspended structure.Consider the setup shown in Fig. 1, in which a single electron is confined in a GaAs double dot structure that is embedded inside a freestanding slab. With advances in novel nanofabrication technology, quantum dots can now be embedded into the suspended structure. 20,21 Most of the structure is spatially separated from most of the substrate such tha...

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“…[ [15][16][17] The advantage of our large subband-spacings is that this transition is shifted to larger magnetic fields allowing a better resolution even in a measurement at a higher temperature of of an Al 0.8 Ga 0.2 As sacrificial layer [18,19] . The active layer incorporates a , defining the QPC, which can be capacitively controlled by applying voltages to adjacent 2DES areas (sidegates G1 and G2) [20] .…”

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Freely suspended quantum point contacts

Rössler

Herz

Bichler

et al. 2010

Solid State Communications

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We present a versatile design of freely suspended quantum point contacts with particular large one-dimensional subband quantization energies of up to Narrow constrictions define quantum point contacts that are capacitively controlled via local in-plane side gates. Employing transport spectroscopy, we investigate the transition from electrostatic subbands to Landau-quantization in a perpendicular magnetic field.The large subband quantization energies allow us to utilize a wide magnetic field range and thereby observe a large exchange splitted spin-gap of the two lowest Landau-levels.

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In situ control of electron gas dimensionality in freely suspended semiconductor membranes

Cited by 19 publications

References 15 publications

Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers

Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers

Decoherence of a charge qubit embedded inside a suspended phonon cavity

Freely suspended quantum point contacts

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