36 research outputs found
Piezospectroscopic measurement of high-frequency vibrations in a pulse-tube cryostat
Vibrations in cryocoolers are a recurrent concern to the end user. They
appear in different parts of the acoustic spectrum depending on the
refrigerator type, Gifford McMahon or pulse-tube, and with a variable coupling
strength to the physical system under interest. Here, we use the
piezospectroscopic effect in rare-earth doped crystals at low temperature as a
high resolution, contact-less probe for the vibrations. With this optical
spectroscopic technique, we obtain and analyze the vibration spectrum up to
700kHz of a 2kW pulse-tube cooler. We attempt an absolute calibration based on
known experimental parameters to make our method partially quantitative and to
provide a possible comparison with other well-established techniques
Evaluation of a stoichiometric rare earth crystal for quantum computing
This thesis presents a spectroscopic study of the 7F0 ---t5D0 transition of Eu3+ in EuC13 ·6H2 0,
which is used to evaluate the potential performance of a quantum com puting system implemented in
EuCla·6H2 0 and, more generally, in stoichiometric rare earth crystals.
EuC13 ·6H2 0 has one of the narrowest optical inhomogeneous linewidths of any solid but this
linewidth is shown to be still much larger than that required for practical quantum computing in a
rare earth crystal. To assess the possibility of reducing the linwidth, the contributions of
isotopic impurities to both the optical linewidth and line structure were investigated, and ligand
isotopes were identified as a major source of both inhomogeneous broadening and structure on the
optical transition, suggesting that the linewidth could be substantially reduced by isotopi cally
purifying EuC13 ·6H20. The effect of ligand isotopes on the optical lifetime and coherence time was
also investigated. It was found that fully deuterating the crystal to EuC13·6D20 substantially
improves both the lifetime and coherence time.
The satellite lines formed in the optical spectrum of a rare earth crystal when
it is doped with another rare earth are proposed as qubits. A crucial step in char acterising
EuCla ·6H20 for quantum computing is associating these satellite lines in EuC13 ·6H2 0 with
crystallographic sites. A new method for associating sites with lines, which works for low symmetry
crystals such as EuC13·6H20, is presented. This method involves modelling the splitting of the
ground state hyperfine levels caused by the magnetic dipole-dipole interaction between a Kramers
dopant and the Eu3+ ion. Using this method, most of the outer satellite lines in rare earth doped
EuCla·6H2 0 were assigned to crystallographic sites.
It has been proposed that the electronic interactions between these satellite lines
be used to enact two-qubit gates in a rare earth quantum computer. These interac tions were
measured between a number of different satellite lines using a new two laser spectral holeburning
technique. Interactions of up to 46.081±0.005 MHz were observed, and this was the first time that
electronic interactions between weakly coupled rare earth ions had been measured. The two most
common interactions identified between rare earth ions in solids are electric dipole-dipole and
exchange, but the observed interactions are stronger than expected from a electric dipole-dipole
model and occur at too large a distance to be superexchange.
It is shown that the development of a moderate-sized quantum processor, one
with more than 10 qubits, in a stoichiometric rare earth crystal is feasible provided that the
optical inhomogeneous linewidth is reduced below 1MHz. Demonstrations of three or four qubit
devices should be possible using existing materials
Quantum information processing using frozen core Y 3+ spins in Eu 3+ :Y 2 SiO 5
In this paper, we present a method to investigate and control the dynamics of the nearby host nuclear spins (the 'frozen core') about a rare-earth ion doped in a crystal. Optically detected, double quantum magnetic resonance measurements were conducted on Eu3+ Y2SiO5. The distinct magnetic resonant frequencies of nearby Y3+ spins were measured along with the lifetime and coherence time of an individual Y3+ spin. We demonstrate an entangling gate between the Eu3+ spins and a Y3+ spin associated with a particular position. Further, we propose a method to initialize the Y3+ spin states, enabling the Y3+ spins to be used as a quantum resource for quantum information applications.This work was supported by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (Grant No. CE110001027). MZ is supported by the Science, Technology and Innovation Commission of Shenzhen Municipality (No. ZDSYS20170303165926217, No.
JCYJ20170412152620376)) and Guangdong Innovative and Entrepreneurial Research Team Program (Grant No. 2016ZT06D348). RLA is a recipient of an Australian Research Council Discovery Early Career Researcher Award (project No. DE170100099)
Ultranarrow Optical Inhomogeneous Linewidth in a Stoichiometric Rare-Earth Crystal
We obtain a low optical inhomogeneous linewidth of 25 MHz in the stoichiometric rare-earth crystal EuCl3·6H2O by isotopically purifying the crystal in Cl35. With this linewidth, an important limit for stoichiometric rare-earth crystals is surpassed: the hyperfine structure of Eu153 is spectrally resolved, allowing the whole population of Eu1533+ ions to be prepared in the same hyperfine state using hole-burning techniques. This material also has a very high optical density, and can have long coherence times when deuterated. This combination of properties offers new prospects for quantum information applications. We consider two of these: quantum memories and quantum many-body studies. We detail the improvements in the performance of current memory protocols possible in these high optical depth crystals, and describe how certain memory protocols, such as off-resonant Raman memories, can be implemented for the first time in a solid-state system. We explain how the strong excitation-induced interactions observed in this material resemble those seen in Rydberg systems, and describe how these interactions can lead to quantum many-body states that could be observed using standard optical spectroscopy techniques
Method for assigning satellite lines to crystallographic sites in rare-earth crystals
We describe an experimental technique for associating the satellite lines in a rare-earth optical spectrum caused by a defect with the rare-earth ions in crystal sites around that defect. This method involves measuring the hyperfine splitting caused by
Optical memory bandwidth and multiplexing capacity in the erbium telecommunication window
We study the bandwidth and multiplexing capacity of an erbium-doped optical
memory for quantum storage purposes. We concentrate on the protocol ROSE
(Revival of a Silenced Echo) because it has the largest potential multiplexing
capacity. Our analysis is applicable to other protocols that involve strong
optical excitation. We show that the memory performance is limited by
instantaneous spectral diffusion and we describe how this effect can be
minimised to achieve optimal performance
Microwave to optical photon conversion via fully concentrated rare-earth-ion crystals
Most investigations of rare-earth ions in solids for quantum information have used crystals where the rare-earth ion is a dopant. Here, we analyze the conversion of quantum information from microwave photons to optical frequencies using crystals where the rare-earth ions, rather than being dopants, are part of the host crystal. These concentrated crystals are attractive for frequency conversion because of their large ion densities and small linewidths. We show that conversion with both high efficiency and large bandwidth is possible in these crystals. In fact, the collective coupling between the rare-earth ions and the optical and microwave cavities is large enough that the limitation on the bandwidth of the devices will instead be the spacing between magnon modes in the crystal
Quantum processing with ensembles of rare-earth ions in a stoichiometric crystal
We describe a method for creating small quantum processors in a crystal stoichiometric in an optically active rare-earth ion. The crystal is doped with another rare earth, creating an ensemble of identical clusters of surrounding ions, whose optical and hyperfine frequencies are uniquely determined by their spatial position in the cluster. Ensembles of ions in each unique position around the dopant serve as qubits, with strong local interactions between ions in different qubits. These ensemble qubits can each be used as a quantum memory for light, and we show how the interactions between qubits can be used to perform linear operations on the stored photonic state. We also describe how these ensemble qubits can be used to enact, and study, error correction.R.L.A. acknowledges support from an Australian
Research Council Discovery Early Career Researcher Award
(Project No. DE170100099). This work was supported by the
Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (Grant No.
CE110001027)
Optimising the Efficiency of a Quantum Memory based on Rephased Amplified Spontaneous Emission
We studied the recall efficiency as a function of optical depth of rephased
amplified spontaneous emission (RASE), a protocol for generating entangled
light. The experiments were performed on the
transition in the rare-earth doped crystal
Pr:YSiO, using a four-level echo sequence between four
hyperfine levels to rephase the emission. Rephased emission was observed for
optical depths in the range of = 0.8 to 2.0 with a maximum rephasing
efficiency of 14 % observed while incorporating spin storage. This efficiency
is a significant improvement over the previously reported non-classical result
but is well short of the predicted efficiency. We discuss the possible
mechanisms limiting the protocol's performance, and suggest ways to overcome
these limits.Comment: 5 pages, 5 figure