Principal Investigator: Professor Stefan KröllThe Project
Quantum memories and Interfaces: Rare Earth ion
doped solids
The goal of this project is to develop quantum memories
based upon efficient storage and reconstruction of photon encoded qubits in
optically dense, rare-earth ion doped solids using controlled reversible
inhomogeneous broadening (CRIB).
This memory implementation will store quantum and
classical states of light in suitably prepared ensemble of ions.
Inhomogeneous broadening in rare-earth ion doped solids is due to the
different local environments experienced by the dopant ions. A narrowband
absorption line will be prepared on a nonabsorbing background by selectively
pumping ions with undesirable absorption frequencies to long-lived hyperfine
levels. The remaining absorption feature will be inhomogeneously broadened,
for instance using a Stark shift, and the input pulse to be stored will be
absorbed, leaving the dopant ions in an excited state. The controlled
inhomogeneous broadening mechanism will then be “switched off”. Retrieval of
the pulse will be accomplished by implementing a necessary position
dependent phase shift and reversing the controlled inhomogeneous broadening,
thus inducing the necessary rephasing. The readout pulse will then propagate
in the opposite direction to the input pulse. This readout procedure is an
implementation of the photon-echo effect: an instantaneous change in some of
the atomic properties such that the field is restored.
During the initial stages of this project, the
suitability of different rare-earth ion doped solids will be assessed by
partners based at the Lund Institute of Technology and the University of
Geneva. Long term objectives include storage of classical optical pulses,
single photons and single photon time-bin qubits.
Quantum Simulation and Control: Rare-earth ion doped
crystals
Universal quantum computation is a demanding task,
requiring implementation of quantum gates with extremely high precision.
Control of quantum evolution will be required for error correction,
decoherence control and application of quantum gates. This project will look
at optimal pulse sequences for the control of quantum computation operations
in rare-earth ion doped crystals.
Similarly to the CRIB technique described above, the
experimental work carried out in this project will be carried out using
rare-earth ion doped crystals, cooled to cryogenic temperatures using liquid
helium. Hyperfine levels in the ground electronic states of the ions will
form the qubit representations. Qubits are distinguishable because they have
different transition frequencies due to the inhomogeneous broadening caused
by the crystal environment. Qubit A – qubit B interactions are accomplished
by inducing a permanent dipole moment on an ion A when it is excited to an
excited state using an optical pulse. This changes the local electric field
and shifts the absorption frequency of the surrounding ions (B).
The project focus will be on the control of single
dopant ions using optical pulses. Optimal pulse shapes will be developed by
researchers at TU-Munich for two and three qubit
operations. These sequences will be tested by researchers at the University
of Lund, using pulses generated using acousto-optic modulators, controlled
by arbitrary function generators. Read out will be implemented by
transferring the data qubit value to a ‘bus ion’, whose state will then be
characterised. Additionally, research into the effects of doubly doped
crystals will be carried out. When a second dopant is introduced to a
crystal, it will affect the dephasing mechanisms present within the system.
Investigation of such doubly doped crystals will provide insight into the
dephasing mechanisms of crystal impurities. Such information is important
for scaling the architecture to include more qubits.
Other QAP Activities
- Optimal Control of Quantum Systems with Finite Degrees of Freedom:
Spins and beyond, with TU-Munich
List of Publications
QAP
J. Wesenberg, K. Mølmer, L. Rippe and S. Kröll,
Scalable designs for quantum computing with rare-earth ion doped crystals,
submitted to Phys. Rev. A
quant-ph/0601141
L. Rippe, B. Julsgaard, A. Walther and S. Kröll, Laser
stabilization to inhomogeneously broadened transitions, submitted to Phys.
Rev. A
quant-ph/0611056
A. Kalachev and S. Kröll, Coherent control of
collective spontaneous emission in an extended atomic ensemble and quantum
state storage, Phys. Rev. A 74 023814 (2006)
quant-ph/0606155
O. Guillot-Nol et al.,
Hyperfine structure,
optical dephasing and spectral-hole lifetime in a single crystal of
Pr3+:La2(WO4)3, Phys. Rev. B 75 205110 (2007)
Related Work
J. Wesenberg, K. Mølmer, L. Rippe
and S. Kröll, Scalable designs for quantum computing with rare-earth ion
doped crystals, submitted to Phys. Rev. A
quant-ph/0601141
V. Palm, M. Pärs, J. Kikas, M. Nilsson and S. Kröll,
Single-molecule linewidths of terrylene in incommensurate biphenyl:
thermocycling and time-resolved experiments, J. Luminescence 127
218 (2007)
Group website
Quantum memories and Interfaces: Rare Earth ion doped solids
The goal of this project is to develop quantum memories based upon efficient storage and reconstruction of photon encoded qubits in optically dense, rare-earth ion doped solids using controlled reversible inhomogeneous broadening (CRIB).
This memory implementation will store quantum and classical states of light in suitably prepared ensemble of ions. Inhomogeneous broadening in rare-earth ion doped solids is due to the different local environments experienced by the dopant ions. A narrowband absorption line will be prepared on a nonabsorbing background by selectively pumping ions with undesirable absorption frequencies to long-lived hyperfine levels. The remaining absorption feature will be inhomogeneously broadened, for instance using a Stark shift, and the input pulse to be stored will be absorbed, leaving the dopant ions in an excited state. The controlled inhomogeneous broadening mechanism will then be “switched off”. Retrieval of the pulse will be accomplished by implementing a necessary position dependent phase shift and reversing the controlled inhomogeneous broadening, thus inducing the necessary rephasing. The readout pulse will then propagate in the opposite direction to the input pulse. This readout procedure is an implementation of the photon-echo effect: an instantaneous change in some of the atomic properties such that the field is restored.
During the initial stages of this project, the suitability of different rare-earth ion doped solids will be assessed by partners based at the Lund Institute of Technology and the University of Geneva. Long term objectives include storage of classical optical pulses, single photons and single photon time-bin qubits.
Quantum Simulation and Control: Rare-earth ion doped crystals
Universal quantum computation is a demanding task, requiring implementation of quantum gates with extremely high precision. Control of quantum evolution will be required for error correction, decoherence control and application of quantum gates. This project will look at optimal pulse sequences for the control of quantum computation operations in rare-earth ion doped crystals.
Similarly to the CRIB technique described above, the experimental work carried out in this project will be carried out using rare-earth ion doped crystals, cooled to cryogenic temperatures using liquid helium. Hyperfine levels in the ground electronic states of the ions will form the qubit representations. Qubits are distinguishable because they have different transition frequencies due to the inhomogeneous broadening caused by the crystal environment. Qubit A – qubit B interactions are accomplished by inducing a permanent dipole moment on an ion A when it is excited to an excited state using an optical pulse. This changes the local electric field and shifts the absorption frequency of the surrounding ions (B).
The project focus will be on the control of single dopant ions using optical pulses. Optimal pulse shapes will be developed by researchers at TU-Munich for two and three qubit operations. These sequences will be tested by researchers at the University of Lund, using pulses generated using acousto-optic modulators, controlled by arbitrary function generators. Read out will be implemented by transferring the data qubit value to a ‘bus ion’, whose state will then be characterised. Additionally, research into the effects of doubly doped crystals will be carried out. When a second dopant is introduced to a crystal, it will affect the dephasing mechanisms present within the system. Investigation of such doubly doped crystals will provide insight into the dephasing mechanisms of crystal impurities. Such information is important for scaling the architecture to include more qubits.
Other QAP Activities
- Optimal Control of Quantum Systems with Finite Degrees of Freedom: Spins and beyond, with TU-Munich
List of Publications
QAP
J. Wesenberg, K. Mølmer, L. Rippe and S. Kröll, Scalable designs for quantum computing with rare-earth ion doped crystals, submitted to Phys. Rev. A quant-ph/0601141
L. Rippe, B. Julsgaard, A. Walther and S. Kröll, Laser stabilization to inhomogeneously broadened transitions, submitted to Phys. Rev. A quant-ph/0611056
A. Kalachev and S. Kröll, Coherent control of collective spontaneous emission in an extended atomic ensemble and quantum state storage, Phys. Rev. A 74 023814 (2006) quant-ph/0606155
O. Guillot-Nol et al., Hyperfine structure, optical dephasing and spectral-hole lifetime in a single crystal of Pr3+:La2(WO4)3, Phys. Rev. B 75 205110 (2007)
Related Work
J. Wesenberg, K. Mølmer, L. Rippe and S. Kröll, Scalable designs for quantum computing with rare-earth ion doped crystals, submitted to Phys. Rev. A quant-ph/0601141
V. Palm, M. Pärs, J. Kikas, M. Nilsson and S. Kröll, Single-molecule linewidths of terrylene in incommensurate biphenyl: thermocycling and time-resolved experiments, J. Luminescence 127 218 (2007)