197 research outputs found
Quantum Algorithmic Readout in Multi-Ion Clocks
Optical clocks based on ensembles of trapped ions offer the perspective of
record frequency uncertainty with good short-term stability. Most suitable
atomic species lack closed transitions for fast detection such that the clock
signal has to be read out indirectly through transferring the quantum state of
clock ions to co-trapped logic ions by means of quantum logic operations. For
ensembles of clock ions existing methods for quantum logic readout require a
linear overhead in either time or the number of logic ions. Here we report a
quantum algorithmic readout whose overhead scales logarithmically with the
number of clock ions in both of these respects. We show that the readout
algorithm can be implemented with a single application of a multi-species
quantum gate, which we describe in detail for a crystal of Aluminum and Calcium
ions.Comment: 4 pages + 7 pages appendix; 5 figures; v3: published versio
Quantum Noise for Faraday Light Matter Interfaces
In light matter interfaces based on the Faraday effect quite a number of quantum information protocols have been successfully demonstrated. In order to further increase the performance and fidelities achieved in these protocols a deeper understanding of the relevant noise and decoherence processes needs to be gained. In this article we provide for the first time a complete description of the decoherence from spontaneous emission. We derive from first principles the effects of photons being spontaneously emitted into unobserved modes. Our results relate the resulting decay and noise terms in effective equations of motion for collective atomic spins and the forward propagating light modes to the full atomic level structure. We illustrate and apply our results to the case of a quantum memory protocol. Our results can be applied to any suitable atomic species, and the general approach taken in this article can be applied to light matter interfaces and quantum memories based on different mechanisms
Quantum teleportation between light and matter
Quantum teleportation is an important ingredient in distributed quantum
networks, and can also serve as an elementary operation in quantum computers.
Teleportation was first demonstrated as a transfer of a quantum state of light
onto another light beam; later developments used optical relays and
demonstrated entanglement swapping for continuous variables. The teleportation
of a quantum state between two single material particles (trapped ions) has now
also been achieved. Here we demonstrate teleportation between objects of a
different nature - light and matter, which respectively represent 'flying' and
'stationary' media. A quantum state encoded in a light pulse is teleported onto
a macroscopic object (an atomic ensemble containing 10^12 caesium atoms).
Deterministic teleportation is achieved for sets of coherent states with mean
photon number (n) up to a few hundred. The fidelities are 0.58+-0.02 for n=20
and 0.60+-0.02 for n=5 - higher than any classical state transfer can possibly
achieve. Besides being of fundamental interest, teleportation using a
macroscopic atomic ensemble is relevant for the practical implementation of a
quantum repeater. An important factor for the implementation of quantum
networks is the teleportation distance between transmitter and receiver; this
is 0.5 metres in the present experiment. As our experiment uses propagating
light to achieve the entanglement of light and atoms required for
teleportation, the present approach should be scalable to longer distances.Comment: 23 pages, 8 figures, incl. supplementary informatio
Quantum entanglement and teleportation in pulsed cavity-optomechanics
Entangling a mechanical oscillator with an optical mode is an enticing and
yet a very challenging goal in cavity optomechanics. Here we consider a pulsed
scheme to create Einstein-Podolsky-Rosen-type entanglement between a
traveling-wave light pulse and a mechanical oscillator. The entanglement can be
verified unambiguously by a pump-probe sequence of pulses. In contrast to
schemes that work in a steady-state regime under a continuous-wave drive, this
protocol is not subject to stability requirements that normally limit the
strength of achievable entanglement. We investigate the protocol's performance
under realistic conditions, including mechanical decoherence, in full detail.
We discuss the relevance of a high mechanical Qf product for entanglement
creation and provide a quantitative statement on which magnitude of the Qf
product is necessary for a successful realization of the scheme. We determine
the optimal parameter regime for its operation and show it to work in current
state-of-the-art systems.Comment: 10 pages, 2 figure
Sequential Generation of Matrix-Product States in Cavity QED
We study the sequential generation of entangled photonic and atomic
multi-qubit states in the realm of cavity QED. We extend the work of C. Schoen
et al. [Phys. Rev. Lett. 95, 110503 (2005)], where it was shown that all states
generated in a sequential manner can be classified efficiently in terms of
matrix-product states. In particular, we consider two scenarios: photonic
multi-qubit states sequentially generated at the cavity output of a
single-photon source and atomic multi-qubit states generated by their
sequential interaction with the same cavity mode.Comment: 11 page
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Hybrid Quantum Devices and Quantum Engineering
We discuss prospects of building hybrid quantum devices involving elements of atomic and
molecular physics, quantum optics and solid-state elements with the attempt to combine
advantages of the respective systems in compatible experimental setups. In particular, we summarize our recent work on quantum hybrid devices and briefly discuss recent ideas for quantum networks. These include interfacing of molecular quantum memory with circuit QED, and using nanomechanical elements strongly coupled to qubits represented by electronic spins, as well as single atoms or atomic ensembles.Physic
Pulsed quantum optomechanics
Studying mechanical resonators via radiation pressure offers a rich avenue
for the exploration of quantum mechanical behavior in a macroscopic regime.
However, quantum state preparation and especially quantum state reconstruction
of mechanical oscillators remains a significant challenge. Here we propose a
scheme to realize quantum state tomography, squeezing and state purification of
a mechanical resonator using short optical pulses. The scheme presented allows
observation of mechanical quantum features despite preparation from a thermal
state and is shown to be experimentally feasible using optical microcavities.
Our framework thus provides a promising means to explore the quantum nature of
massive mechanical oscillators and can be applied to other systems such as
trapped ions.Comment: 9 pages, 4 figure
Precision spectroscopy by photon-recoil signal amplification
Precision spectroscopy of atomic and molecular ions offers a window to new
physics, but is typically limited to species with a cycling transition for
laser cooling and detection. Quantum logic spectroscopy has overcome this
limitation for species with long-lived excited states. Here, we extend quantum
logic spectroscopy to fast, dipole-allowed transitions and apply it to perform
an absolute frequency measurement. We detect the absorption of photons by the
spectroscopically investigated ion through the photon recoil imparted on a
co-trapped ion of a different species, on which we can perform efficient
quantum logic detection techniques. This amplifies the recoil signal from a few
absorbed photons to thousands of fluorescence photons. We resolve the line
center of a dipole-allowed transition in 40Ca+ to 1/300 of its observed
linewidth, rendering this measurement one of the most accurate of a broad
transition. The simplicity and versatility of this approach enables
spectroscopy of many previously inaccessible species.Comment: 25 pages, 6 figures, 1 table, updated supplementary information,
fixed typo
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