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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

A photonic quantum gate based on electrically controlled strong cavity coupling between a single nanocrystal quantum dot and an ultrahigh Q silica microcavity

Mark J. Fernée, Halina H. Rubinsztein-Dunlop

Published Dec 28, 2005• 0 citations
Publisher

Abstract

We investigate the use of nanocrystal quantum dots as a versatile quantum bus element for preparing various quantum resources for use in photonic quantum technologies. The ability to Stark tune nanocrystal quantum dots allows an important degree of control over the cavity QED interaction. Using this property along with the bi-exciton transition, we demonstrate a photonic CNOT interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large bi-exciton losses. These results are discussed in light of the current state-of-the-art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and micro-cavity design. Such a gate could serve as an active element in photonic-based quantum technologies.

DOI
10.1117/12.651741

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•Jun 19, 2012•11 citations
We investigate the use of nanocrystal quantum dots as a versatile quantum bus element for preparing various quantum resources for use in photonic quantum technologies. The ability to Stark tune nanocrystal quantum dots allows an important degree of control over the cavity QED interaction. Using this property along with the bi-exciton transition, we demonstrate a photonic CNOT interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large bi-exciton losses. These results are discussed in light of the current state-of-the-art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and micro-cavity design. Such a gate could serve as an active element in photonic-based quantum technologies.
We investigate the use of nanocrystal quantum dots as a quantum bus element for preparing various quantum resources for use in photonic quantum technologies. Using the Stark-tuning property of nanocrystal quantum dots as well as the biexciton transition, we demonstrate a photonic controlled-NOT (CNOT) interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large biexciton losses. These results are discussed in light of the current state of the art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and microcavity design. Such a gate could serve as an active element in photonic-based quantum technologies.
Generating strong interactions between single quanta of light and matter is central to quantum information science, and a key component of quantum computers and long-distance quantum networks. In quantum information processing, these interactions are required to create elementary logic operations (quantum gates) between stationary matter quantum bits (qubits) and photonic qubits that can be transmitted over long distances. Efficient quantum gates between photonic and matter qubits are a crucial enabler for a broad range of applications that include robust quantum networks, nondestructive quantum measurements, and strong photon-photon interactions. So far these qubit-photon gates have been achieved using single atoms and at microwave frequencies in circuit QED systems. Their implementation with solidstate quantum emitters, however, has remained a difficult challenge. We demonstrate that the qubit state of a photon can be controlled by a single solid-state qubit composed of a quantum dot (QD) strongly coupled to an optical nanocavity. We show that the QD acts as a coherently controllable qubit system that conditionally flips the polarization of a photon reflected from the cavity mode on picosecond timescales. This operation implements a controlled NOT (cNOT) logic gate between the QD and the incident photon, which is a universal quantum operation that can serve as a general light-matter interface for remote entanglements and quantum computations. Our results represent an important step towards an all solid-state implementation of quantum networks and quantum computers, and provide a versatile approach for controlling and probing interactions between a photon and a single quantum emitter on ultra-fast timescales.
We investigate theoretically two-photon processes in a microcavity containing one quantum dot in the strong-coupling regime. The cavity mode can be tuned to resonantly drive the two-photon transition between the ground and the biexciton states while the exciton states are far-off resonance due to the biexciton binding energy. We study the steady state of the quantum dot and cavity field in presence of a continuous incoherent pumping. We identify the regime where the system acts as two-photon emitter and discuss the feasibility and performance of realistic single quantum-dot devices for two-photon lasing.
The strong-coupling regime of cavity-quantum-electrodynamics (cQED) represents the light-matter interaction at the fully quantum level. Adding a single photon shifts the resonance frequencies, a profound nonlinearity. cQED is a test-bed of quantum optics and the basis of photon-photon and atom-atom entangling gates. At microwave frequencies, success in cQED has had a transformative effect. At optical frequencies, the gates are potentially much faster; the photons can propagate over long distances; and the photons can be detected easily, ideal features for quantum networks. Following pioneering work on single atoms, solid-state implementations using semiconductor quantum dots are emerging, an important prospect for quantum technology. We present here a gated, ultralow-loss microcavity-device which forms a highly coherent photon−-−quantum-dot interface with a cooperativity of C=150C=150C=150. The gates allow both the quantum dot charge state and resonance frequency to be controlled electrically; crucially, they eliminate the noise-source which has complicated quantum dot cQED in the past −-− scattering from the bare microcavity mode even at the quantum dot-microcavity resonance. Even in the microcavity, the quantum dot has a linewidth close to the radiative limit. In addition to a very pronounced avoided-crossing in the spectral domain, we observe a clear coherent exchange of a single energy-quantum between the ``atom" and cavity in the time domain (vacuum Rabi-oscillations). Decoherence arises predominantly via the atom and photon loss-channels. The coherence is exploited to probe the transitions between the singly- and doubly-excited photon-atom system via photon-statistics spectroscopy. We propose this system as a platform for quantum technology, for instance a photon-photon entangling gate.
Exploiting the giant optical circular birefringence induced by the double-sided quantum-dot–cavity system, we construct a deterministic hybrid hyper-controlled-not (hyper-CNOT) gate, in which the spatial-mode and polarization states of a photon act as the two control qubits, whereas two stationary electron spins in quantum dots confined inside the optical microcavities serve as the two target qubits. In our scheme, the control qubits are easily manipulated with simple optical elements and the target qubits are suitable for storage and processing use. With our hybrid hyper-CNOT gates, we design a high-capacity direct transmission quantum communication network which requires neither the establishment of entanglement between remote locations nor the use of long-lived quantum memories. We discuss the feasibility and efficiency of our hybrid hyper-CNOT gate, concluding that it is feasible with current technology.
This thesis presents a viable route towards the implementation of quantum computing utilizing quantum dots embedded in optical microcavities. Following the introduction of the big picture and long-term visionary goal, general concepts fundamental to this field of research are described: quantum dots and microcavities, forming the physical system explored; and cavity quantum electrodynamics, the theoretical language used to describe their interaction.\n\nThe physical structure and the optical mode composition in oxide-apertured micropillar cavities is analyzed. Permanent tuning methods achieving polarization degenerate cavities resonant with a quantum dot transition are illustrated. Active positioning of single quantum dots is developed providing an accuracy suitable to measure the interaction between a quantum dot and a cavity in the strong coupling limit. The possibility to waveguide-couple photonic crystal cavities on the same sample is explored. A theoretical description of the quantum-dot confined electron dynamics is presented. \nPresented are ideas how a hybrid quantum system could serve for implementation of a controlled NOT gate, and therewith be the building block for a quantum computer, exploiting the weak coupling regime. A Bell-state analyzer is the second scheme that is discussed. \nResults from reflection spectroscopy measurements on single quantum dots in a micropillar cavity are presented.