Three orders of magnitude cavity-linewidth narrowing in a rare-earth-ion-doped crystal cavity, in... more Three orders of magnitude cavity-linewidth narrowing in a rare-earth-ion-doped crystal cavity, induced by strong intra-cavity dispersion caused by off-resonant interaction with dopant ions is demonstrated. The strong dispersion is created by semi-permanent but rapidly reprogrammable changes of the rare earth absorption profiles using optical pumping techniques. Several cavity modes are shown within the spectral transmission window. Potential applications are discussed.
EQEC '05. European Quantum Electronics Conference, 2005.
A scheme for highly efficient storage and recall of single- and few-photon wave-packets in solid ... more A scheme for highly efficient storage and recall of single- and few-photon wave-packets in solid state materials (here inorganic crystals doped with rare-earth ions) is presented. The scheme is supported by experimental data showing that single-photon absorption effects can be observed in these materials and also how the materials can be tailored for the quantum state storage and reconstruction operation using suitably selected excitation pulses.
Accurate and efficient quantum control in the presence of constraints and decoherence is a requir... more Accurate and efficient quantum control in the presence of constraints and decoherence is a requirement and a challenge in quantum information processing. Shortcuts to adiabaticity, originally proposed to speed up the slow adiabatic process, have nowadays become versatile toolboxes for preparing states or controlling the quantum dynamics. Unique shortcut designs are required for each quantum system with intrinsic physical constraints, imperfections, and noise. Here, we implement fast and robust control for the state preparation and state engineering in a rare-earth ions system. Specifically, the interacting pulses are inversely engineered and further optimized with respect to inhomogeneities of the ensemble and the unwanted interaction with other qubits. We demonstrate that our protocols surpass the conventional adiabatic schemes, by reducing the decoherence from the excited-state decay and inhomogeneous broadening. The results presented here are applicable to other noisy intermediat...
Observation of a magnetic-field-induced resonance in the homogeneous dephasing time for the D-1(2... more Observation of a magnetic-field-induced resonance in the homogeneous dephasing time for the D-1(2)-H-3(4) transition in Pr3+:YAlO3. Physical Review B (Condensed Matter), 54(14), 9834-9839.
European Quantum Electronics Conference, Jun 22, 2003
The paper reports on the experimental realization on the possibility of isolating ions in a selec... more The paper reports on the experimental realization on the possibility of isolating ions in a selected frequency channel. In the scheme, this interaction is mediated by the change in permanent dipole moment experienced by the rare-earth ions when they are optically excited from the ground state to an excited state. The change in dipole moment changes the electric field experienced by ions situated close to the excited ion, thus their absorption frequencies are changed. The important aspect, in order to use this frequency shift for controlled logic, is that the shift is large enough for ions, originally resonant with a certain laser frequency, to be shifted out of resonance with this laser field. Excitation induced frequency shifts are experimentally observed, which opens the way for the realisation of the first quantum gate in this type of solid state materials.
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011
Ultrasound-modulated optical tomography (UOT) is a promising method to go beyond the 5cm “hard de... more Ultrasound-modulated optical tomography (UOT) is a promising method to go beyond the 5cm “hard depth” detection limit[1]. The principal idea of UOT is to use the acousto-optic effect, where the ultrasound shifts the frequency of the light. The resolution of UOT (∼ mm) is determined by the ultrasonic wave focus and duration, and the UOT contrast is determined by the optical properties of the tissue [2].
Two-pulse photon-echo measurements on the 0.1 at. % Pr'+:YA10, H4-'D& transition suggest that the... more Two-pulse photon-echo measurements on the 0.1 at. % Pr'+:YA10, H4-'D& transition suggest that the relaxation time depends on the density of excited states created by the excitation pulses. The dependence of the relaxation time on the intensity of each excitation pulse shows that our results are inconsistent with instantaneous spectral diffusion, a model often invoked in this type of experiment, where excited states created by the second pulse chiefly inhuence the relaxation time. A homogeneous linewidth contribution, noted in previous work as being of unknown origin, is eliminated at low excitation fluences.
Abstract Ultrasound modulated optical tomography allows optical imaging with ultrasound resolutio... more Abstract Ultrasound modulated optical tomography allows optical imaging with ultrasound resolution in highly scattering tissue, with application to early tumor detection. Slow light provides additional time domain filtering to enhance detection sensitivity.
ABSTRACT A 56% efficiency quantum memory is created by inserting a 1% efficiency memory in a low-... more ABSTRACT A 56% efficiency quantum memory is created by inserting a 1% efficiency memory in a low-finesse cavity. Changing the memory absorption profile by optical pumping decreases the cavity mode-spacing by >4 orders of magnitude.
Photon-echo-relaxation measurements made on the 'H4-'Po transition of 0.01 at. % Pr'+:YAG (where ... more Photon-echo-relaxation measurements made on the 'H4-'Po transition of 0.01 at. % Pr'+:YAG (where YAG represents yttrium aluminum garnet), 'H4-'D2 transition in 0.1 at. % Pr'+:YA103, and Fo-'Do transition in 0.25 at. % Eu'+:YA103 show that the photon-echo relaxation rate increases when the intensities of the excitation pulses are increased. Although a part of the relaxation-rate increase in Pr'+:YAG may be attributed to an instantaneous spectral diff'usion (ISD) in which the presence of excited neighboring Pr'+ ions change the local field and the absorption frequency of the rare-earth ions, our data deviate significantly from the ISD-model predictions. An additional intensity-dependent relaxation mechanism is required to explain the results.
We demonstrate experimentally a quantum memory scheme for the storage of weak coherent light puls... more We demonstrate experimentally a quantum memory scheme for the storage of weak coherent light pulses in an inhomogeneously broadened optical transition in a Pr 3+ : YSO crystal at 2.1 K. Precise optical pumping using a frequency stable (≈1kHz linewidth) laser is employed to create a highly controllable Atomic Frequency Comb (AFC) structure. We report single photon storage and retrieval efficiencies of 25%, based on coherent photon echo type re-emission in the forward direction. The coherence property of the quantum memory is proved through interference between a super Gaussian pulse and the emitted echo. Backward retrieval of the photon echo emission has potential for increasing storage and recall efficiency.
We present spectral hole-burning measurements on the 879 nm, 4 I 9/2 → 4 F 3/2 transition in Nd 3... more We present spectral hole-burning measurements on the 879 nm, 4 I 9/2 → 4 F 3/2 transition in Nd 3+ : YVO 4. We observe antiholes in the spectrum along with long lived spectral holes, which demonstrates optical pumping between the ground state Zeeman levels. The spectral holes are narrow ͑homogeneous linewidth of 63 kHz͒ at 2.1 K with a 300 mT applied magnetic field. We also perform preliminary spectral tailoring in this material by creating a 40 MHz wide transmission window in the inhomogeneous absorption. These results show the potential of the Zeeman levels in Nd doped materials to be used for spectral tailoring for quantum and classical information processing.
... PHYSICAL REVIEW B 71, 149902 E 2005 Erratum: Hole-burning techniques for isolation and study ... more ... PHYSICAL REVIEW B 71, 149902 E 2005 Erratum: Hole-burning techniques for isolation and study of individual hyperfine transitions in inhomogeneously broadened solids demonstrated in Pr3+ : Y2SiO5 [Phys. Rev B 70, 214116 (2004)] Mattias Nilsson, Lars Rippe, Stefan Kr? ...
Most of the experiments related to quantum information applications, involving rare-earth doped i... more Most of the experiments related to quantum information applications, involving rare-earth doped inorganic crystals, are performed on yttrium orthosilicate single crystals. The work presented here is motivated by the search of new compounds which can be used in the field of quantum computing and/or quantum storage. Relaxation times and hyperfine structure of the 3 H 4 ͑0͒ → 1 D 2 ͑0͒ transition in 1.4% Pr 3+ :La 2 ͑WO 4 ͒ 3 at 4 K have been measured by photon-echo and spectral-hole-burning techniques. The hyperfine splittings of the ground 3 H 4 ͑0͒ and the excited 1 D 2 ͑0͒ states are 14.9± 0.1 MHz, 24.6± 0.1 MHz and 5.0± 0.1 MHz, 7.3± 0.1 MHz, respectively. An inhomogeneous linewidth of 18.8± 0.1 GHz was measured. A homogeneous linewidth of 25.3± 2.0 kHz was obtained with or without an external magnetic field of about 14 mT. The fluorescence dynamics of the 1 D 2 level obtained by a direct excitation in the 3 H 4 → 1 D 2 transition gives a nonexponential decay which indicates energy-transfer processes. This decay can be accurately fitted by the Inokuti-Hirayama model ͓J. Chem. Phys. 43, 1978 ͑1965͔͒ with a radiative lifetime of 61± 1 s giving a minimal homogeneous linewidth of 2.6 kHz. The spectral-hole lifetime due to population redistribution within the ground hyperfine levels is 16± 2 s. The results obtained for the La 2 ͑WO 4 ͒ 3 compound make this crystal an interesting host for quantum applications.
Hole-burning techniques for isolation and study of individual hyperfine transitions in inhomogene... more Hole-burning techniques for isolation and study of individual hyperfine transitions in inhomogeneously broadened solids demonstrated in Pr3+: Y2SiO5. Physical Review B (Condensed Matter and Materials Physics), 70(21).
Due to inhomogeneous broadening, the absorption lines of rare-earth-ion dopands in crystals are m... more Due to inhomogeneous broadening, the absorption lines of rare-earth-ion dopands in crystals are many order of magnitudes wider than the homogeneous linewidths. Several ways have been proposed to use ions with different inhomogeneous shifts as qubit registers, and to perform gate operations between such registers by means of the static dipole coupling between the ions. In this paper we show that in order to implement high-fidelity quantum gate operations by means of the static dipole interaction, we require the participating ions to be strongly coupled, and that the density of such strongly coupled registers in general scales poorly with register size. Although this is critical to previous proposals which rely on a high density of functional registers, we describe architectures and preparation strategies that will allow scalable quantum computers based on rareearth-ion doped crystals.
In this paper initial experiments towards constructing simple quantum gates in a solid state mate... more In this paper initial experiments towards constructing simple quantum gates in a solid state material are presented. Instead of using specially tailored materials, the aim is to select a subset of randomly distributed ions in the material, which have the interaction necessary to control each other and therefore can be used to do quantum logic operations. The experimental results demonstrate that part of an inhomogeneously broadened absorption line can be selected as a qubit and that a subset of ions in the material can control the resonance frequency of other ions. This opens the way for the construction of quantum gates in rare-earth-ion doped crystals.
Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimula... more Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimulated photon echoes in a rare-earth-doped crystal (0.1 at. % Pr3+:LaF3). Two spatially encoded laser pulses (pictures) resonant with the 3 PO-3 H 4 transition of Pr 3 + were stored by focusing the image pulses sequentially into the Pr 3 +:LaF 3 crystal. The stored information is retrieved and processed by a third read pulse, generating the echo that is the spatial convolution or correlation of the input images. Application of this scheme to high-speed pattern recognition is discussed.
Erasure of data stored by use of photon echoes has been investigated as a function of data writin... more Erasure of data stored by use of photon echoes has been investigated as a function of data writing time and data storage time. The results clarify the requirements on laser phase and frequency stability for performing photon-echo data erasure. The analysis of phase and frequency stability of a light source by the photon-echo erasure process is illustrated. A theoretical analysis emphasizing the physical processes that affect the erasure efficiency as well as an extensive discussion of possible error sources are given. Finally, an approach to bit-selective photon-echo data erasure that is insensitive to laser phase and frequency fluctuations is suggested.
Three orders of magnitude cavity-linewidth narrowing in a rare-earth-ion-doped crystal cavity, in... more Three orders of magnitude cavity-linewidth narrowing in a rare-earth-ion-doped crystal cavity, induced by strong intra-cavity dispersion caused by off-resonant interaction with dopant ions is demonstrated. The strong dispersion is created by semi-permanent but rapidly reprogrammable changes of the rare earth absorption profiles using optical pumping techniques. Several cavity modes are shown within the spectral transmission window. Potential applications are discussed.
EQEC '05. European Quantum Electronics Conference, 2005.
A scheme for highly efficient storage and recall of single- and few-photon wave-packets in solid ... more A scheme for highly efficient storage and recall of single- and few-photon wave-packets in solid state materials (here inorganic crystals doped with rare-earth ions) is presented. The scheme is supported by experimental data showing that single-photon absorption effects can be observed in these materials and also how the materials can be tailored for the quantum state storage and reconstruction operation using suitably selected excitation pulses.
Accurate and efficient quantum control in the presence of constraints and decoherence is a requir... more Accurate and efficient quantum control in the presence of constraints and decoherence is a requirement and a challenge in quantum information processing. Shortcuts to adiabaticity, originally proposed to speed up the slow adiabatic process, have nowadays become versatile toolboxes for preparing states or controlling the quantum dynamics. Unique shortcut designs are required for each quantum system with intrinsic physical constraints, imperfections, and noise. Here, we implement fast and robust control for the state preparation and state engineering in a rare-earth ions system. Specifically, the interacting pulses are inversely engineered and further optimized with respect to inhomogeneities of the ensemble and the unwanted interaction with other qubits. We demonstrate that our protocols surpass the conventional adiabatic schemes, by reducing the decoherence from the excited-state decay and inhomogeneous broadening. The results presented here are applicable to other noisy intermediat...
Observation of a magnetic-field-induced resonance in the homogeneous dephasing time for the D-1(2... more Observation of a magnetic-field-induced resonance in the homogeneous dephasing time for the D-1(2)-H-3(4) transition in Pr3+:YAlO3. Physical Review B (Condensed Matter), 54(14), 9834-9839.
European Quantum Electronics Conference, Jun 22, 2003
The paper reports on the experimental realization on the possibility of isolating ions in a selec... more The paper reports on the experimental realization on the possibility of isolating ions in a selected frequency channel. In the scheme, this interaction is mediated by the change in permanent dipole moment experienced by the rare-earth ions when they are optically excited from the ground state to an excited state. The change in dipole moment changes the electric field experienced by ions situated close to the excited ion, thus their absorption frequencies are changed. The important aspect, in order to use this frequency shift for controlled logic, is that the shift is large enough for ions, originally resonant with a certain laser frequency, to be shifted out of resonance with this laser field. Excitation induced frequency shifts are experimentally observed, which opens the way for the realisation of the first quantum gate in this type of solid state materials.
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011
Ultrasound-modulated optical tomography (UOT) is a promising method to go beyond the 5cm “hard de... more Ultrasound-modulated optical tomography (UOT) is a promising method to go beyond the 5cm “hard depth” detection limit[1]. The principal idea of UOT is to use the acousto-optic effect, where the ultrasound shifts the frequency of the light. The resolution of UOT (∼ mm) is determined by the ultrasonic wave focus and duration, and the UOT contrast is determined by the optical properties of the tissue [2].
Two-pulse photon-echo measurements on the 0.1 at. % Pr'+:YA10, H4-'D& transition suggest that the... more Two-pulse photon-echo measurements on the 0.1 at. % Pr'+:YA10, H4-'D& transition suggest that the relaxation time depends on the density of excited states created by the excitation pulses. The dependence of the relaxation time on the intensity of each excitation pulse shows that our results are inconsistent with instantaneous spectral diffusion, a model often invoked in this type of experiment, where excited states created by the second pulse chiefly inhuence the relaxation time. A homogeneous linewidth contribution, noted in previous work as being of unknown origin, is eliminated at low excitation fluences.
Abstract Ultrasound modulated optical tomography allows optical imaging with ultrasound resolutio... more Abstract Ultrasound modulated optical tomography allows optical imaging with ultrasound resolution in highly scattering tissue, with application to early tumor detection. Slow light provides additional time domain filtering to enhance detection sensitivity.
ABSTRACT A 56% efficiency quantum memory is created by inserting a 1% efficiency memory in a low-... more ABSTRACT A 56% efficiency quantum memory is created by inserting a 1% efficiency memory in a low-finesse cavity. Changing the memory absorption profile by optical pumping decreases the cavity mode-spacing by >4 orders of magnitude.
Photon-echo-relaxation measurements made on the 'H4-'Po transition of 0.01 at. % Pr'+:YAG (where ... more Photon-echo-relaxation measurements made on the 'H4-'Po transition of 0.01 at. % Pr'+:YAG (where YAG represents yttrium aluminum garnet), 'H4-'D2 transition in 0.1 at. % Pr'+:YA103, and Fo-'Do transition in 0.25 at. % Eu'+:YA103 show that the photon-echo relaxation rate increases when the intensities of the excitation pulses are increased. Although a part of the relaxation-rate increase in Pr'+:YAG may be attributed to an instantaneous spectral diff'usion (ISD) in which the presence of excited neighboring Pr'+ ions change the local field and the absorption frequency of the rare-earth ions, our data deviate significantly from the ISD-model predictions. An additional intensity-dependent relaxation mechanism is required to explain the results.
We demonstrate experimentally a quantum memory scheme for the storage of weak coherent light puls... more We demonstrate experimentally a quantum memory scheme for the storage of weak coherent light pulses in an inhomogeneously broadened optical transition in a Pr 3+ : YSO crystal at 2.1 K. Precise optical pumping using a frequency stable (≈1kHz linewidth) laser is employed to create a highly controllable Atomic Frequency Comb (AFC) structure. We report single photon storage and retrieval efficiencies of 25%, based on coherent photon echo type re-emission in the forward direction. The coherence property of the quantum memory is proved through interference between a super Gaussian pulse and the emitted echo. Backward retrieval of the photon echo emission has potential for increasing storage and recall efficiency.
We present spectral hole-burning measurements on the 879 nm, 4 I 9/2 → 4 F 3/2 transition in Nd 3... more We present spectral hole-burning measurements on the 879 nm, 4 I 9/2 → 4 F 3/2 transition in Nd 3+ : YVO 4. We observe antiholes in the spectrum along with long lived spectral holes, which demonstrates optical pumping between the ground state Zeeman levels. The spectral holes are narrow ͑homogeneous linewidth of 63 kHz͒ at 2.1 K with a 300 mT applied magnetic field. We also perform preliminary spectral tailoring in this material by creating a 40 MHz wide transmission window in the inhomogeneous absorption. These results show the potential of the Zeeman levels in Nd doped materials to be used for spectral tailoring for quantum and classical information processing.
... PHYSICAL REVIEW B 71, 149902 E 2005 Erratum: Hole-burning techniques for isolation and study ... more ... PHYSICAL REVIEW B 71, 149902 E 2005 Erratum: Hole-burning techniques for isolation and study of individual hyperfine transitions in inhomogeneously broadened solids demonstrated in Pr3+ : Y2SiO5 [Phys. Rev B 70, 214116 (2004)] Mattias Nilsson, Lars Rippe, Stefan Kr? ...
Most of the experiments related to quantum information applications, involving rare-earth doped i... more Most of the experiments related to quantum information applications, involving rare-earth doped inorganic crystals, are performed on yttrium orthosilicate single crystals. The work presented here is motivated by the search of new compounds which can be used in the field of quantum computing and/or quantum storage. Relaxation times and hyperfine structure of the 3 H 4 ͑0͒ → 1 D 2 ͑0͒ transition in 1.4% Pr 3+ :La 2 ͑WO 4 ͒ 3 at 4 K have been measured by photon-echo and spectral-hole-burning techniques. The hyperfine splittings of the ground 3 H 4 ͑0͒ and the excited 1 D 2 ͑0͒ states are 14.9± 0.1 MHz, 24.6± 0.1 MHz and 5.0± 0.1 MHz, 7.3± 0.1 MHz, respectively. An inhomogeneous linewidth of 18.8± 0.1 GHz was measured. A homogeneous linewidth of 25.3± 2.0 kHz was obtained with or without an external magnetic field of about 14 mT. The fluorescence dynamics of the 1 D 2 level obtained by a direct excitation in the 3 H 4 → 1 D 2 transition gives a nonexponential decay which indicates energy-transfer processes. This decay can be accurately fitted by the Inokuti-Hirayama model ͓J. Chem. Phys. 43, 1978 ͑1965͔͒ with a radiative lifetime of 61± 1 s giving a minimal homogeneous linewidth of 2.6 kHz. The spectral-hole lifetime due to population redistribution within the ground hyperfine levels is 16± 2 s. The results obtained for the La 2 ͑WO 4 ͒ 3 compound make this crystal an interesting host for quantum applications.
Hole-burning techniques for isolation and study of individual hyperfine transitions in inhomogene... more Hole-burning techniques for isolation and study of individual hyperfine transitions in inhomogeneously broadened solids demonstrated in Pr3+: Y2SiO5. Physical Review B (Condensed Matter and Materials Physics), 70(21).
Due to inhomogeneous broadening, the absorption lines of rare-earth-ion dopands in crystals are m... more Due to inhomogeneous broadening, the absorption lines of rare-earth-ion dopands in crystals are many order of magnitudes wider than the homogeneous linewidths. Several ways have been proposed to use ions with different inhomogeneous shifts as qubit registers, and to perform gate operations between such registers by means of the static dipole coupling between the ions. In this paper we show that in order to implement high-fidelity quantum gate operations by means of the static dipole interaction, we require the participating ions to be strongly coupled, and that the density of such strongly coupled registers in general scales poorly with register size. Although this is critical to previous proposals which rely on a high density of functional registers, we describe architectures and preparation strategies that will allow scalable quantum computers based on rareearth-ion doped crystals.
In this paper initial experiments towards constructing simple quantum gates in a solid state mate... more In this paper initial experiments towards constructing simple quantum gates in a solid state material are presented. Instead of using specially tailored materials, the aim is to select a subset of randomly distributed ions in the material, which have the interaction necessary to control each other and therefore can be used to do quantum logic operations. The experimental results demonstrate that part of an inhomogeneously broadened absorption line can be selected as a qubit and that a subset of ions in the material can control the resonance frequency of other ions. This opens the way for the construction of quantum gates in rare-earth-ion doped crystals.
Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimula... more Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimulated photon echoes in a rare-earth-doped crystal (0.1 at. % Pr3+:LaF3). Two spatially encoded laser pulses (pictures) resonant with the 3 PO-3 H 4 transition of Pr 3 + were stored by focusing the image pulses sequentially into the Pr 3 +:LaF 3 crystal. The stored information is retrieved and processed by a third read pulse, generating the echo that is the spatial convolution or correlation of the input images. Application of this scheme to high-speed pattern recognition is discussed.
Erasure of data stored by use of photon echoes has been investigated as a function of data writin... more Erasure of data stored by use of photon echoes has been investigated as a function of data writing time and data storage time. The results clarify the requirements on laser phase and frequency stability for performing photon-echo data erasure. The analysis of phase and frequency stability of a light source by the photon-echo erasure process is illustrated. A theoretical analysis emphasizing the physical processes that affect the erasure efficiency as well as an extensive discussion of possible error sources are given. Finally, an approach to bit-selective photon-echo data erasure that is insensitive to laser phase and frequency fluctuations is suggested.
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Papers by Stefan Kröll