Atom-by-atom assembly of defect-free
one-dimensional cold atom arrays
Manuel Endres,1,2*† Hannes Bernien,1 Alexander Keesling,1 Harry Levine,1*
Eric R. Anschuetz,1 Alexandre Krajenbrink,1‡ Crystal Senko,1 Vladan Vuletic,3
Markus Greiner,1 Mikhail D. Lukin1
The realization of large-scale fully controllable quantum systems is an exciting frontier in
modern physical science. We use atom-by-atom assembly to implement a platform for the
deterministic preparation of regular one-dimensional arrays of individually controlled cold
atoms. In our approach, a measurement and feedback procedure eliminates the entropy
associated with probabilistic trap occupation and results in defect-free arrays of more than 50
atoms in less than 400 milliseconds. The technique is based on fast, real-time control of 100
optical tweezers, which we use to arrange atoms in desired geometric patterns and to
maintain these configurations by replacing lost atoms with surplus atoms from a reservoir.
This bottom-up approach may enable controlled engineering of scalable many-body systems
for quantum information processing, quantum simulations, and precision measurements.
The detection and manipulation of individ- ual quantum particles, such as atoms or photons, isnowroutinelyperformedinmany quantum physics experiments (1, 2); how- ever, retaining the same control in large-scale systems remains an outstanding challenge.
For example, major efforts are currently aimed at
scaling up ion-trap and superconducting platforms, where high-fidelity quantum computing
operations have been demonstrated in registers
consisting of several qubits (3, 4). In contrast, ultracold quantum gases composed of neutral atoms
offer inherently large system sizes. However, arbitrary single-atom control is highly demanding,
and its realization is further limited by the slow
evaporative cooling process necessary to reach
quantum degeneracy. Only in recent years has
individual particle detection (5, 6) and basic single-spin control (7) been demonstrated in low-entropy
optical lattice systems.
Here, we demonstrate atom-by-atom assembly
of large defect-free one-dimensional (1D) arrays
of cold neutral atoms (8, 9).
We use optical microtraps to directly extract
individual atoms from a laser-cooled cloud (10–12)
and employ recently demonstrated trapping tech-
niques (13–16) and single-atom position control
(17–20) to create desired atomic configurations.
Central to our approach is the use of single-atom
detection and real-time feedback (17, 20) to elim-
inate the entropy associated with the probabi-
listic trap loading (10) [currently limited to 90%
loading probability even with advanced techniques
(21–23)]. Related to the fundamental concept of
“Maxwell’s demon” (8, 9), this method allows
us to rapidly create large defect-free arrays and,
when supplemented with appropriate atom-atom
interactions (15, 16, 24–30), provides a potential
platform for scalable experiments with individu-
ally controlled neutral atoms.
The experimental protocol is illustrated in Fig.
1A. An array of 100 tightly focused optical tweezers
is loaded from a laser-cooled cloud. The col-
lisional blockade effect ensures that each in-
dividual tweezer is either empty or occupied by
a single atom (10). A first high-resolution image
yields single-atom-resolved information about the
trap occupation, which we use to identify empty
traps and to switch them off. The remaining
occupied traps are rearranged into a regular,
defect-free array, and we detect the final atom
configuration with a second high-resolution image.
Our implementation relies on fast, real-time control of the tweezer positions (Fig. 1B), which we
achieve by employing an acousto-optic deflector
(AOD) that we drive with a multitone radio-frequency (RF) signal.
This generates an array of deflected beams,
each controlled by its own RF tone (15, 16). The
resulting beam array is then focused into our
vacuum chamber and forms an array of optical
tweezers, each with a Gaussian waist of ≈ 900 nm,
a wavelength of 809 nm, and a trap depth of
U=kB ≈ 0:9 mK [Boltzmann constant (kB)] that
is homogeneous across the array within 2% (31).
The tweezer array is loaded from a laser-cooled
cloud of Rubidium-87 atoms in a magneto-optical
trap (MOT). After the loading procedure, we let
the MOT cloud disperse and we detect the occupation of the tweezers with fluorescence imaging. Fast, single-shot, single-atom-resolved detection
with 20-ms exposure is enabled by a sub-Doppler
laser-cooling configuration that remains active
during the remainder of the sequence (31) (see
Fig. 2, A to C). Our fluorescence count statistics
show that individual traps are either empty or
occupied by a single atom (10, 31), and we find
probabilistically filled arrays with an average
single-atom loading probability of p ≈ 0:6 (see
Figs. 2A and 3A).
The central part of our scheme involves the
rearrangement procedure for assembling defect-free arrays (31) (see Fig. 1A). In the first step,
1Department of Physics, Harvard University, Cambridge, MA
02138, USA. 2Division of Physics, Mathematics, and
Astronomy, California Institute of Technology, Pasadena, CA
91125, USA. 3Department of Physics and Research
Laboratory of Electronics, Massachusetts Institute of
Technology, Cambridge, MA 02139, USA.
*These authors contributed equally to this work. †Corresponding
author. Email: email@example.com ‡Present address: CNRS-Laboratoire de Physique Theorique de l’Ecole Normale Superieure,
24 Rue L’Homond, 75231 Paris Cedex, France.
Fig. 1. Protocol for creating
defect-free arrays. (A) A first
image identifies optical microtraps loaded with a single
atom, and empty traps are
turned off. The loaded traps are
moved to fill in the empty sites,
and a second image verifies the
success of the operation.
(B) The trap array is produced
by an acousto-optic deflector
(AOD) and imaged with a 1:1
telescope onto a 0.5-NA
microscope objective, which
creates an array of tightly
focused optical tweezers in a
vacuum chamber. An identical
microscope objective is aligned
to image the same focal plane.
A dichroic mirror allows us
to view the trap light on a
(CCD) while simultaneously
detecting the atoms via fluorescence imaging on an
camera (EMCCD). The rearrangement protocol is realized through fast feedback onto the multitone
radio-frequency (RF) field driving the AOD.