arXiv subjects

A. Imamoglu

Publications and source records attributed to A. Imamoglu.

45 records · Page 3Linked to original sources

arXiv2003

Controlling a mesoscopic spin environment by quantum bit manipulation

We present a unified description of cooling and manipulation of a mesoscopic bath of nuclear spins via coupling to a single quantum system of electronic spin (quantum bit). We show that a bath cooled by the quantum bit rapidly saturates. Although the resulting saturated states of the spin bath (``dark states'') generally have low degrees of polarization and purity, their symmetry properties make them a valuable resource for the coherent manipulation of quantum bits. Specifically, we demonstrate that the dark states of nuclear ensembles can be used to coherently control the system-bath interaction and to provide a robust, long-lived quantum memory for qubit states.

cond-mat.mes-hall↗

arXiv2003

Laser cooling of a nanomechanical resonator mode to its quantum ground state

We show that it is possible to cool a nanomechanical resonator mode to its ground state. The proposed technique is based on resonant laser excitation of a phonon sideband of an embedded quantum dot. The strength of the sideband coupling is determined directly by the difference between the electron-phonon couplings of the initial and final states of the quantum dot optical transition. Possible applications of the technique we describe include generation of non-classical states of mechanical motion.

cond-mat.mes-hall↗

arXiv2003

Optical pumping of quantum dot nuclear spins

An all-optical scheme to polarize nuclear spins in a single quantum dot is analyzed. The hyperfine interaction with randomly oriented nuclear spins presents a fundamental limit for electron spin coherence in a quantum dot; by cooling the nuclear spins, this decoherence mechanism could be suppressed. The proposed scheme is inspired by laser cooling methods of atomic physics and implements a "controlled Overhauser effect" in a zero-dimensional structure.

cond-mat.mes-hall↗

arXiv2002

High efficiency photon counting using stopped light

Single-photon detection and photon counting play a central role in a large number of quantum communication and computation protocols. While the efficiency of state-of-the-art photo-detectors is well below the desired limits, quantum state measurements in trapped ions can be carried out with efficiencies approaching 100%. Here, we propose a method that can in principle achieve ideal photon counting, by combining the techniques of photonic quantum memory and ion-trap fluorescence detection: after mapping the quantum state of a propagating light pulse onto metastable collective excitations of a trapped cold atomic gas, it is possible to monitor the resonance fluorescence induced by an additional laser field that only couples to the metastable excited state. Even with a photon collection/detection efficiency as low as 10%, it is possible to achieve photon counting with efficiency approaching 100%.

quant-ph↗

arXiv2001

Photon Correlation Spectroscopy of a Single Quantum Dot

We report photon correlation measurements that allow us to observe unique signatures of biexcitons in a single self-assembled InAs quantum dot. Photon correlation measurements of biexciton emission exhibit both bunching and antibunching under continuous-wave excitation while only antibunching is observed under pulsed excitation. Cross-correlation between biexciton and single-exciton peaks reveal highly asymmetric features, demonstrating that biexciton and exciton emissions have strong correlations due to cascaded emission. The anticipated correlation between the polarization of exciton and biexciton emissions however, is absent under our excitation conditions. Photon correlation measurements also provide evidence for the identification of the charged exciton emission.

cond-mat↗

arXiv2001

Quantum Dot Cavity-QED in the Presence of Strong Electron-Phonon Interactions

A quantum dot strongly coupled to a single high finesse optical microcavity mode constitutes a new fundamental system for quantum optics. Here, the effect of exciton-phonon interactions on reversible quantum-dot cavity coupling is analysed without making Born-Markov approximation. The analysis is based on techniques that have been used to study the ``spin boson'' Hamiltonian. Observability of vacuum-Rabi splitting depends on the strength and the frequency dependence of the spectral density function characterizing the interactions with phonons, both of which can be influenced by phonon confinement.

quant-ph↗

arXiv1999

Nonlinear Optics and Quantum Entanglement of Ultra-Slow Single Photons

Two light pulses propagating with ultra-slow group velocities in a coherently prepared atomic gas exhibit dissipation-free nonlinear coupling of an unprecedented strength. This enables a single-photon pulse to coherently control or manipulate the quantum state of the other. Processes of this kind result in generation of entangled states of radiation field and open up new prospectives for quantum information processing.

quant-ph↗

arXiv1999

Photon-photon interactions in cavity electromagnetically induced transparency

Dissipation-free photon-photon interaction at the single photon level is studied in the context of cavity electromagnetically induced transparency (EIT). For a single multilevel atom exhibiting EIT in the strong cavity-coupling regime, the anharmonicity of the atom-cavity system has an upper bound determined by single atom-photon coupling strength. Photon blockade is inferred to occur for both single and multi-atom cases from the behaviour of transition rates between dressed states of the system. Numerical calculations of the second order coherence function indicate that photon antibunching in both single and two-atom cases are strong and comparable.

quant-ph↗

arXiv1999

Quantum information processing using quantum dot spins and cavity-QED

The electronic spin degrees of freedom in semiconductors typically have decoherence times that are several orders of magnitude longer than other relevant timescales. A solid-state quantum computer based on localized electron spins as qubits is therefore of potential interest. Here, a scheme that realizes controlled interactions between two distant quantum dot spins is proposed. The effective long-range interaction is mediated by the vacuum field of a high finesse microcavity. By using conduction-band-hole Raman transitions induced by classical laser fields and the cavity-mode, parallel controlled-not operations and arbitrary single qubit rotations can be realized. Optical techniques can also be used to measure the spin-state of each quantum dot.

quant-ph↗