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Saturated Absorption for a Magneto-Optical Atom Trap as a Step toward Atomic Dipole Traps in a Diffraction Pattern from a Circular Aperture

Andrew Ferdinand

Published Jan 1, 2011• 2 citations
OpenAlex

Abstract

Neutral atom quantum computing is a promising avenue toward the realization of a physical quantum computer. The diffraction pattern formed by laser light immediately behind a circular aperture can be used as optical atomic dipole traps, and has the potential to be scaled up to create a two dimensional array of individually addressable qubit sites. In working towards experimental demonstration of the dipole traps, we are constructing a MOT. The function of the MOT is to cool and trap 87Rb in a localized cloud in our vacuum chamber, which will be used to load the dipole traps. One critical aspect to the functioning of the MOT is the precise tuning of the trapping laser to the red of the F=2→F’=3 hyperfine transition and the pump laser to the F=1→F’=2 hyperfine transition. We have successfully constructed a saturated absorption apparatus which works to distinguish the hyperfine structure of Rb within the Doppler broadened transition peaks. The saturated absorption scans serve to correlate the voltage applied to the piezo with the laser light frequencies causing hyperfine transitions in Rb, allowing for the precise tuning of the lasers needed to trap atoms.

Related papers

Polarization-dependent atomic dipole traps behind a circular aperture for neutral-atom quantum computing

Katharina Gillen-Christandl, Bert Copsey

The neutral-atom quantum computing community has successfully implemented almost all necessary steps for constructing a neutral-atom quantum computer. We present computational results of a study aimed at solving the remaining problem of creating a quantum memory with individually addressable sites for quantum computing. The basis of this quantum memory is the diffraction pattern formed by laser light incident on a circular aperture. Very close to the aperture, the diffraction pattern has localized bright and dark spots that can serve as red-detuned or blue-detuned atomic dipole traps. These traps are suitable for quantum computing even for moderate laser powers. In particular, for moderate laser intensities ($~100$ W/${\mathrm{cm}}^{2}$) and comparatively small detunings ($~1000$--10 000 linewidths), trap depths of $~1$ mK and trap frequencies of several to tens of kilohertz are achieved. Our results indicate that these dipole traps can be moved by tilting the incident laser beams without significantly changing the trap properties. We also explored the polarization dependence of these dipole traps. We developed a code that calculates the trapping potential energy for any magnetic substate of any hyperfine ground state of any alkali-metal atom for any laser detuning much smaller than the fine-structure splitting for any given electric field distribution. We describe details of our calculations and include a summary of different notations and conventions for the reduced matrix element and how to convert it to SI units. We applied this code to these traps and found a method for bringing two traps together and apart controllably without expelling the atoms from the trap and without significant tunneling probability between the traps. This approach can be scaled up to a two-dimensional array of many pinholes, forming a quantum memory with single-site addressability, in which pairs of atoms can be brought together and apart for two-qubit gates for quantum computing.

Physical Review A•Feb 9, 2011•13 citations

Developing an Imaging System to Monitor Atom Traps for Neutral Atom Quantum Computing

Jenna Valdez

Quantum computing exploits the laws of quantum mechanics to exponentially increase computing rate for certain processes. A realized quantum computer could break encryptions and simulate large quantum systems previously unbreakable and unattainable with classical computers. Neutral atom quantum computing is a viable candidate for building these devices that satisfies four of the five criteria for a successful quantum computer. We are exploring a novel method in creating neutral atom qubits that involves a magneto-optical trap and a dipole trap created in the diffraction pattern behind an array of pinholes. The magneto-optical trap works to cool the atoms and centralize them into a cold-atom cloud in an ultra-high vacuum chamber. Laser light is then projected into the chamber through the array of pinholes, trapping the cooled atoms in light traps. In order to test the efficiency of our trapping method, I have developed an imaging system that monitors the atoms. The system is comprised of a high-speed camera that takes images of the trap while a photodiode measures the fluorescence signal from the cold-atom cloud. These measurements are used to determine the number of atoms successfully trapped, how long they remain trapped, and the trap frequency. This paper presents the details and process of developing the complete imaging system.

•Jan 1, 2017•0 citations

Achieving Laser Wavelength Stability for Use in Neutral Atom Quantum Computing

Jennifer H. Rushing

Quantum computing may still be decades away from realization but the pieces necessary for the construction of the first quantum chip are beginning to come together. One piece still eluding researchers is the ability to address individual atoms within a scalable quantum chip structure. The resolution to this issue may be found in any one of several promising implementations, including the use of neutral atoms trapped in 2D optical lattices. One method of constructing such lattices, which has been shown to be computationally viable, employs the diffraction pattern just behind a circular aperture. Laser wavelength stability plays a crucial role in this approach, which entails constructing a 2D optical lattice with an array of pinholes, populating the lattice with atoms collected by a magneto optical trap (MOT), and manipulating the atoms trapped within the lattice structure for quantum computations. Experimental work was done toward achieving the laser wavelength stability required for these tasks. First, we investigated inadequate temperature control of the laser diodes and a thermal mass issue attributed to the laser mounts was resolved. We proceeded to analyze the electronics of the laser locking feedback system, which were failing to hold the lasers steady at a desired wavelength. Several noise sources contributing to signal instability were identified and eliminated, but drifting of the error signal was persistent. A subsequent fix was then made to the locking electronics and sufficient laser wavelength stability was demonstrated when atoms were trapped for the first time in the Cal Poly MOT on September 2, 2011.

•Jan 1, 2011•0 citations

Optical Trapping and Cooling of Single Atoms

D.A. van der Flier

Single atoms are a promising candidate for the creation of a scalable quantum computer. Neutral atoms trapped by optical fields are especially encouraging due to the full controllability of the trap potential. Single neutral atoms trapped within a fibre-fibre cavity allow us to strongly couple atoms and photons. This creates an efficient atom-photon interface which can compensate for the short state transfer distance inherent of neutral atoms. A spatial light modulator allows for the creation and manipulation of an array of these single atom traps.\n\nIn this research we create a setup to cool and trap neutral rubidium-87 atoms by a combination of a magneto-optical trap (MOT) and a dipole trap. The dipole trap uses a strongly focused, far red-detuned laser, which enables us to trap single atoms via the collisional blockade regime. These traps are realised within a novel glass cell, allowing for great optical access.\n\nThe MOT in this setup is able to trap (4.27 +/- 0.10) * 10^3 atoms with a density of (7.89 +/- 0.56) * 10^9 atoms cm^-3 . The MOT temperature is in the order of 100 μK. We also show the manipulation of these properties, allowing us to tailor the MOT. The dipole trap is created with a trap waist of 37 μm, allowing us to trap a cloud of atoms. With the dipole trap we achieve a lifetime of atoms of (34.8 +/- 2.0) ms.

•Jan 1, 2017•0 citations

Monitoring Atom Traps for Neutral Atom Quantum Computing

T. W. Shannon

To increase computing power for numerous practical advantages, scientists are actively researching the field of quantum computing. Neutral atom quantum computing is a promising avenue towards building a quantum computer that satisfies four of the five DiVincenzo criteria. This involves a magneto-optical trap to cool the atoms and move them to a cloud in the center of a vacuum chamber. Then laser light will be shone through an array of pinholes to trap the atoms in an array of dipole traps. In order to ensure the atoms are trapped, I have set up an imaging system that consists of a high speed camera and a photodiode. The imaging system is to be used to determine whether the atoms were successfully trapped, calculate how many were trapped, and measure the temperature of the trap, the trap lifetime, and the trap frequency. Details regarding the setup and programming of this imaging system are presented in this paper.

•Jan 1, 2014•0 citations

Development of a magneto optical trap for Rubidium 87

Huzifa Mohammed Ahamed Mohammed Elnour

ENGLISH ABSTRACT: A Magneto Optical Trap (MOT) is a configuration formed by three orthogonal pairs of counterpropagating circularly polarized laser beams and a magnetic field gradient. A MOT is used to cool, capture and trap large numbers of atoms in vacuum at very low temperature in K range. In this thesis the development of an experimental setup for realising a MOT of 87Rb atoms is presented. The atomic structure of Rb and the theoretical background of laser cooling and magneto optical trapping was reviewed. The influence of rubidium background pressure in the vacuum system, the laser beam size and the power and frequency on the number of the trapped atoms were studied in literature. The trapping and repumping lasers were characterised experimentally. Six circularly polarised trapping beams with equal power were formed and properly aligned to intersect at the center of the trapping cell. Two optical setups were designed and exploited to investigate and optimise the trapping beam polarisation. The repumping laser beam was successfully aligned and colinearly combined into all the trapping beams. Three different experimental setups for saturated absorption spectroscopy were developed. Saturated absorption spectra showing the hyperfine structure of both 85Rb and 87Rb isotopes were measured and are discussed. Using two saturated absorption spectroscopy setups, the frequencies of both lasers were successfully locked to the trapping and repumping transitions of 87Rb respectively. A rectangular trapping cell was designed and attached to the vacuum system. A pressure of about 10­¯7 mbar was achieved. The magnetic field coils were characterised and affixed on both sides of the cell in an anti-Helmholtz configuration. Setups for imaging and quantification of the 87Rb atoms in the MOT were designed. Finally, the procedures for demonstrating a MOT are presented. In conclusion, the current status of the project is reported, with recommendations for the future work.

•Dec 1, 2013•0 citations
Neutral atom quantum computing is a promising avenue toward the realization of a physical quantum computer. The diffraction pattern formed by laser light immediately behind a circular aperture can be used as optical atomic dipole traps, and has the potential to be scaled up to create a two dimensional array of individually addressable qubit sites. In working towards experimental demonstration of the dipole traps, we are constructing a MOT. The function of the MOT is to cool and trap 87Rb in a localized cloud in our vacuum chamber, which will be used to load the dipole traps. One critical aspect to the functioning of the MOT is the precise tuning of the trapping laser to the red of the F=2→F’=3 hyperfine transition and the pump laser to the F=1→F’=2 hyperfine transition. We have successfully constructed a saturated absorption apparatus which works to distinguish the hyperfine structure of Rb within the Doppler broadened transition peaks. The saturated absorption scans serve to correlate the voltage applied to the piezo with the laser light frequencies causing hyperfine transitions in Rb, allowing for the precise tuning of the lasers needed to trap atoms.
The neutral-atom quantum computing community has successfully implemented almost all necessary steps for constructing a neutral-atom quantum computer. We present computational results of a study aimed at solving the remaining problem of creating a quantum memory with individually addressable sites for quantum computing. The basis of this quantum memory is the diffraction pattern formed by laser light incident on a circular aperture. Very close to the aperture, the diffraction pattern has localized bright and dark spots that can serve as red-detuned or blue-detuned atomic dipole traps. These traps are suitable for quantum computing even for moderate laser powers. In particular, for moderate laser intensities ( 100~100 100 W/cm2{\mathrm{cm}}^{2}cm2) and comparatively small detunings ( 1000~1000 1000--10 000 linewidths), trap depths of  1~1 1 mK and trap frequencies of several to tens of kilohertz are achieved. Our results indicate that these dipole traps can be moved by tilting the incident laser beams without significantly changing the trap properties. We also explored the polarization dependence of these dipole traps. We developed a code that calculates the trapping potential energy for any magnetic substate of any hyperfine ground state of any alkali-metal atom for any laser detuning much smaller than the fine-structure splitting for any given electric field distribution. We describe details of our calculations and include a summary of different notations and conventions for the reduced matrix element and how to convert it to SI units. We applied this code to these traps and found a method for bringing two traps together and apart controllably without expelling the atoms from the trap and without significant tunneling probability between the traps. This approach can be scaled up to a two-dimensional array of many pinholes, forming a quantum memory with single-site addressability, in which pairs of atoms can be brought together and apart for two-qubit gates for quantum computing.
Quantum computing exploits the laws of quantum mechanics to exponentially increase computing rate for certain processes. A realized quantum computer could break encryptions and simulate large quantum systems previously unbreakable and unattainable with classical computers. Neutral atom quantum computing is a viable candidate for building these devices that satisfies four of the five criteria for a successful quantum computer. We are exploring a novel method in creating neutral atom qubits that involves a magneto-optical trap and a dipole trap created in the diffraction pattern behind an array of pinholes. The magneto-optical trap works to cool the atoms and centralize them into a cold-atom cloud in an ultra-high vacuum chamber. Laser light is then projected into the chamber through the array of pinholes, trapping the cooled atoms in light traps. In order to test the efficiency of our trapping method, I have developed an imaging system that monitors the atoms. The system is comprised of a high-speed camera that takes images of the trap while a photodiode measures the fluorescence signal from the cold-atom cloud. These measurements are used to determine the number of atoms successfully trapped, how long they remain trapped, and the trap frequency. This paper presents the details and process of developing the complete imaging system.
Quantum computing may still be decades away from realization but the pieces necessary for the construction of the first quantum chip are beginning to come together. One piece still eluding researchers is the ability to address individual atoms within a scalable quantum chip structure. The resolution to this issue may be found in any one of several promising implementations, including the use of neutral atoms trapped in 2D optical lattices. One method of constructing such lattices, which has been shown to be computationally viable, employs the diffraction pattern just behind a circular aperture. Laser wavelength stability plays a crucial role in this approach, which entails constructing a 2D optical lattice with an array of pinholes, populating the lattice with atoms collected by a magneto optical trap (MOT), and manipulating the atoms trapped within the lattice structure for quantum computations. Experimental work was done toward achieving the laser wavelength stability required for these tasks. First, we investigated inadequate temperature control of the laser diodes and a thermal mass issue attributed to the laser mounts was resolved. We proceeded to analyze the electronics of the laser locking feedback system, which were failing to hold the lasers steady at a desired wavelength. Several noise sources contributing to signal instability were identified and eliminated, but drifting of the error signal was persistent. A subsequent fix was then made to the locking electronics and sufficient laser wavelength stability was demonstrated when atoms were trapped for the first time in the Cal Poly MOT on September 2, 2011.
Single atoms are a promising candidate for the creation of a scalable quantum computer. Neutral atoms trapped by optical fields are especially encouraging due to the full controllability of the trap potential. Single neutral atoms trapped within a fibre-fibre cavity allow us to strongly couple atoms and photons. This creates an efficient atom-photon interface which can compensate for the short state transfer distance inherent of neutral atoms. A spatial light modulator allows for the creation and manipulation of an array of these single atom traps.\n\nIn this research we create a setup to cool and trap neutral rubidium-87 atoms by a combination of a magneto-optical trap (MOT) and a dipole trap. The dipole trap uses a strongly focused, far red-detuned laser, which enables us to trap single atoms via the collisional blockade regime. These traps are realised within a novel glass cell, allowing for great optical access.\n\nThe MOT in this setup is able to trap (4.27 +/- 0.10) * 10^3 atoms with a density of (7.89 +/- 0.56) * 10^9 atoms cm^-3 . The MOT temperature is in the order of 100 μK. We also show the manipulation of these properties, allowing us to tailor the MOT. The dipole trap is created with a trap waist of 37 μm, allowing us to trap a cloud of atoms. With the dipole trap we achieve a lifetime of atoms of (34.8 +/- 2.0) ms.
To increase computing power for numerous practical advantages, scientists are actively researching the field of quantum computing. Neutral atom quantum computing is a promising avenue towards building a quantum computer that satisfies four of the five DiVincenzo criteria. This involves a magneto-optical trap to cool the atoms and move them to a cloud in the center of a vacuum chamber. Then laser light will be shone through an array of pinholes to trap the atoms in an array of dipole traps. In order to ensure the atoms are trapped, I have set up an imaging system that consists of a high speed camera and a photodiode. The imaging system is to be used to determine whether the atoms were successfully trapped, calculate how many were trapped, and measure the temperature of the trap, the trap lifetime, and the trap frequency. Details regarding the setup and programming of this imaging system are presented in this paper.
ENGLISH ABSTRACT: A Magneto Optical Trap (MOT) is a configuration formed by three orthogonal pairs of counterpropagating circularly polarized laser beams and a magnetic field gradient. A MOT is used to cool, capture and trap large numbers of atoms in vacuum at very low temperature in K range. In this thesis the development of an experimental setup for realising a MOT of 87Rb atoms is presented. The atomic structure of Rb and the theoretical background of laser cooling and magneto optical trapping was reviewed. The influence of rubidium background pressure in the vacuum system, the laser beam size and the power and frequency on the number of the trapped atoms were studied in literature. The trapping and repumping lasers were characterised experimentally. Six circularly polarised trapping beams with equal power were formed and properly aligned to intersect at the center of the trapping cell. Two optical setups were designed and exploited to investigate and optimise the trapping beam polarisation. The repumping laser beam was successfully aligned and colinearly combined into all the trapping beams. Three different experimental setups for saturated absorption spectroscopy were developed. Saturated absorption spectra showing the hyperfine structure of both 85Rb and 87Rb isotopes were measured and are discussed. Using two saturated absorption spectroscopy setups, the frequencies of both lasers were successfully locked to the trapping and repumping transitions of 87Rb respectively. A rectangular trapping cell was designed and attached to the vacuum system. A pressure of about 10­¯7 mbar was achieved. The magnetic field coils were characterised and affixed on both sides of the cell in an anti-Helmholtz configuration. Setups for imaging and quantification of the 87Rb atoms in the MOT were designed. Finally, the procedures for demonstrating a MOT are presented. In conclusion, the current status of the project is reported, with recommendations for the future work.