<s>
An	O
electron-on-helium	B-Device
qubit	I-Device
is	O
a	O
quantum	O
bit	O
for	O
which	O
the	O
orthonormal	O
basis	O
states	O
|0⟩	O
and	O
|1⟩	O
are	O
defined	O
by	O
quantized	O
motional	O
states	O
or	O
alternatively	O
the	O
spin	O
states	O
of	O
an	O
electron	O
trapped	O
above	O
the	O
surface	O
of	O
liquid	O
helium	O
.	O
</s>
<s>
The	O
electron-on-helium	B-Device
qubit	I-Device
was	O
proposed	O
as	O
the	O
basic	O
element	O
for	O
building	O
quantum	B-Architecture
computers	I-Architecture
with	O
electrons	O
on	O
helium	O
by	O
Platzman	O
and	O
Dykman	O
in	O
1999	O
.	O
</s>
<s>
In	O
2000	O
,	O
Lea	O
and	O
co-authors	O
proposed	O
that	O
the	O
qubit	O
read-out	O
could	O
be	O
achieved	O
using	O
a	O
single	B-Algorithm
electron	I-Algorithm
transistor	I-Algorithm
(	O
SET	O
)	O
device	O
positioned	O
beneath	O
the	O
helium	O
.	O
</s>
<s>
A	O
CCD-like	O
architecture	O
was	O
proposed	O
for	O
the	O
control	O
of	O
the	O
many-qubit	O
system	O
with	O
dipole-dipole	O
interaction	O
allowing	O
two-qubit	O
gate	O
operations	O
for	O
adjacent	O
spins	O
.	O
</s>
<s>
Exchange	B-General_Concept
interaction	I-General_Concept
for	O
adjacent	O
qubits	O
was	O
proposed	O
as	O
a	O
read-out	O
scheme	O
,	O
as	O
demonstrated	O
in	O
semiconductor	O
double-quantum-dot	O
devices	O
.	O
</s>
<s>
In	O
any	O
quantum	B-Architecture
computer	I-Architecture
the	O
decoherence	O
of	O
the	O
qubit	O
wavefunction	O
,	O
due	O
to	O
energy	O
relaxation	O
or	O
dephasing	O
effects	O
,	O
must	O
be	O
limited	O
to	O
a	O
suitably	O
low	O
rate	O
.	O
</s>
<s>
The	O
first	O
trapping	O
and	O
detection	O
of	O
single	O
electrons	O
on	O
helium	O
was	O
demonstrated	O
by	O
Lea	O
and	O
co-workers	O
in	O
2005	O
,	O
using	O
a	O
micron-scale	O
helium-filled	O
trap	O
and	O
a	O
single	B-Algorithm
electron	I-Algorithm
transistor	I-Algorithm
beneath	O
the	O
surface	O
to	O
count	O
the	O
electrons	O
.	O
</s>
<s>
These	O
include	O
ultra-efficient	O
electron	O
clocking	O
in	O
microchannel	O
CCD	B-Algorithm
devices	O
,	O
controlled	O
single	O
electron	O
transport	O
measurements	O
,	O
and	O
the	O
trapping	O
and	O
manipulation	O
of	O
1D	O
electron	O
arrays	O
,	O
In	O
2019	O
,	O
Koolstra	O
and	O
co-workers	O
at	O
the	O
University	O
of	O
Chicago	O
demonstrated	O
the	O
coupling	O
of	O
a	O
single	O
electron	O
on	O
helium	O
to	O
a	O
superconducting	O
microwave	O
cavity	O
,	O
with	O
a	O
coupling	O
strength	O
g/2π	O
~	O
5MHz	O
much	O
larger	O
than	O
the	O
resonator	O
linewidth	O
~	O
0.5MHz	O
.	O
</s>
<s>
In	O
2020	O
,	O
researchers	O
from	O
Michigan	O
State	O
University	O
and	O
EeroQ	O
presented	O
new	O
results	O
and	O
fabrication	O
progress	O
on	O
an	O
electron-on-helium	O
chip	O
design	O
using	O
the	O
lateral	O
motional	O
state	O
of	O
the	O
electron	O
,	O
in	O
frequencies	O
in	O
the	O
5-10	O
GHz	O
range	O
,	O
using	O
a	O
Single-electron	B-Algorithm
transistor	I-Algorithm
readout	O
device	O
.	O
</s>
