Detection of 13.8 dB squeezed vacuum states
by optimizing the interference efficiency and gain
of balanced homodyne detection
Xiaocong Sun (孙小聪)
1
, Yajun Wang (王雅君)
1,2
, Long Tian (田 龙)
1,2
,
Yaohui Zheng (郑耀辉)
1,2,
*, and Kunchi Peng (彭堃墀)
1,2
1
State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi
University, Taiyuan 030006, China
2
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
*Corresponding author: yhzheng@sxu.edu.cn
Received January 8, 2019; accepted March 28, 2019; posted online June 25, 2019
Squeezed states belong to the most prominent non-classical resources. They have compelling applications in
precise measurement, quantum computation, and detection. Here, we report on the direct measurement of
13.8 dB squeezed vacuum states by improving the interference efficiency and gain of balanced homodyne
detection. By employing an auxiliary laser beam, the homodyne visibility is increased to 99.8%. The equivalent
loss of the electronic noise is reduced to 0.05% by integrating a junction field-effect transistor (JFET) buffering
input and another JFET bootstrap structure in the balanced homodyne detector.
OCIS codes: 270.6570, 190.4410.
doi: 10.3788/COL201917.072701.
Squeezed states, which have fewer fluctuations in one
quadrature than vacuum noise at the expense of increased
fluctuations in the other quadrature
[1]
, can be used to
enhance the measurement precision
[2–8]
, increase the
detection sensitivity
[9–12]
, and improve the fault tolerance
performance for quantum information and quantum com-
putation
[13,14]
. A pair of single-mode squeezed states can
be used to generate a cluster state, which can be applied
for greater information capacity and measurement-
based quantum computation
[14,15]
. Moreover, the squeezed
states have been used to increase the sensitivity of the
gravitational wave detector by reducing the quantum
noise
[2,16]
. All of these performance improvements strongly
depend on the measured squeezing level. In terms of large
amounts of quantum noise suppression, the optical
parametric process has been proved to be the most suc-
cessful one
[17–23]
, which has continually held the highest
squeezing strength record. Although the first experimen-
tal demonstration of squeezed states based on the optical
parametric oscillator (OPO) succeeded in 1986
[24]
, in the
following two decades, the dedicated research could only
achieve modest strengths of squeezing
[23–27]
. Until 2007,
researchers at the University of Tokyo took a giant step
forward and obtained a factor of 9 dB quantum noise re-
duction at 860 nm
[22]
. Under the motivation of gravita-
tional waves detection, a 10 dB squeezed vacuum state
was detected for the first time, to the best of our knowl-
edge, at the University of Hanover
[17]
. Subsequently, the
squeezing strength was gradually increased
[18,19]
, reaching
the maximum value of 15 dB at 1064 nm based on peri-
odically poled KTiOPO
4
(PPKTP)
[20]
. With stronger
squeezing, the applications of squeezed states will become
more momentous. In ideal conditions, an infinite squeezing
factor can be generated and detected at the threshold.
However, the measured squeez ing level is usually limited
by photon loss during squeezed states generation, propa-
gation, and detection
[12,28–30]
. The loss that occurs during
the generation of the squeezed state is dependent of the
escape efficiency of the OPO. The escape efficiency can
be increased by reducing the reflectivity of the OPO out-
put coupler. However, this is at the expense of a much
larger OPO threshold, which is usually limited by the
pump power of the laser source. The propagation loss is
determined by the optical components losses from the
OPO output to the photodetector (PD). The detection
efficiency consists of the quantum efficiency of the photo-
diode, the equivalent lo ss of the electronic noise, and the
interference efficiency of balanced homodyne detection
(BHD). Quantum efficiency is the intrinsic parameter of
the photodiode, which cannot be improved by optimizing
the experiment parameters. Therefore, the interference
efficiency and gain of the BHD become the crucial factors
for stronger squeezing factor improvement. In this Letter,
the visibility is increased to 99.8% by using an auxiliary
laser beam technique, where the loss coming from the
interference efficiency is reduced to 0.4%. The electronic
noise of the PD is significantly reduced by a junction
field-effect transistor (JFET) buffering input and another
JFET bootstrap structure. The gain is increased to 33.5 dB
at the local oscillator (LO) of 10.88 mW, where the equiv-
alent loss of the electronic noise corresponds to 0.05%. As a
result, a squeezed vacuum state with non-classical noise
reduction of 13.8 0.2 dB is directly observed.
The experimental setup is shown in Fig.
1. The laser is a
home-made single-frequency laser at 1064 nm. Three
mode cleaners (MCs) are used to improve the properties
COL 17(7), 072701(2019) CHINESE OPTICS LETTERS July 2019
1671-7694/2019/072701(4) 072701-1 © 2019 Chinese Optics Letters