rus
Issue #1/2021
V. M. Petrov, A. V. Shamray, I. V. Ilyichev, P. M. Agruzov, V. V. Lebedev
Broadband Quantum Noise Generator Based on a Controlled Integral Optical Interferometer
Broadband Quantum Noise Generator Based on a Controlled Integral Optical Interferometer
DOI: 10.22184/1993-7296.FRos.2021.15.1.70.75
The work of a quantum noise generator in a band of at least 4 GHz, and with an excess of quantum noise over classical ones by 12–13 dB was demonstrated for the first time. The novel main element of such generator, an optical beam splitter with an electrically controlled splitting ratio, is made in the form of an integrated optical Mach-Zehnder interferometer on a lithium niobate substrate.
The work of a quantum noise generator in a band of at least 4 GHz, and with an excess of quantum noise over classical ones by 12–13 dB was demonstrated for the first time. The novel main element of such generator, an optical beam splitter with an electrically controlled splitting ratio, is made in the form of an integrated optical Mach-Zehnder interferometer on a lithium niobate substrate.
Теги: microwave integrated optical modulators quantum communications quantum noise generator квантовые коммуникации квантовый генератор шума свч интегрально-оптические модуляторы
Broadband Quantum Noise Generator Based on a Controlled Integral Optical Interferometer
V. M. Petrov 1, A. V. Shamray 2, I. V. Ilyichev 2, P. M. Agruzov 2, V. V. Lebedev 2
ITMO National Research University, St. Petersburg, Russia
A. F. Ioffe PTI of RAS, St. Petersburg, Russia
The work of a quantum noise generator in a band of at least 4 GHz, and with an excess of quantum noise over classical ones by 12–13 dB was demonstrated for the first time. The novel main element of such generator, an optical beam splitter with an electrically controlled splitting ratio, is made in the form of an integrated optical Mach-Zehnder interferometer on a lithium niobate substrate.
Keywords: quantum communications, microwave integrated optical modulators, quantum noise generator
Received on: 12.01.2021
Accepted on: 04.02.2021
Introduction
Generating noise as well as generating sequences of random numbers is the backbone of the modern digital economy. Sequences of random numbers are used in security systems, cryptography, scientific research, generating QR codes, blockchains, as well as in games, i. e. in all those practical applications where the task of generating truly random numbers is paramount. In the Russian Federation, special attention is paid to ensuring information security, which follows from the doctrine of “Information security of the Russian Federation”, approved by Decree of the President of the Russian Federation No. 646 dated December 5, 2016.
Our recent successes [1–3] related to the creation of high-quality controllable integrated-optical devices allowed us to create a compact quantum noise generator based on an electrically controlled integrated-optical beam splitter, made according to the Mach-Zehnder interferometer scheme.
Development status
The idea of using a circuit of a quantum noise generator based on vacuum fluctuations (see Fig. 1), containing a local oscillator (laser), an optical beam splitter BS, two photodetectors A, B and a circuit for subtracting electrical signals A-B from photodetectors (balanced detector) is known [4, 5]. The principle of operation of such a device is based on one of the fundamental phenomena of quantum physics – vacuum fluctuations VF [6]. It is generally accepted that the Lamb shift [7] and the Casimir interaction [8, 9] are direct confirmation of the existence of vacuum fluctuations.
Practical implementations of this scheme are described in the literature. In [4], such a scheme was theoretically analyzed, and, based on the element base available at that time, estimates were given of the possible performance of a random number generator based on it – 200 Mbit / s. In [10], an analysis of a similar scheme gave a potential estimate of the performance of 70 Gb / s, and its experimental implementation on volumetric elements made it possible to achieve a noise generation bandwidth of 1.5–2.0 GHz. In [11], the experimentally demonstrated bandwidth of the quantum generation of white noise was approximately 1.9 GHz, in [12] – approximately 0.4…0.5 GHz.
One of the main requirements for the elements of such a device is a high accuracy and stability in time of the division ratio of the beam splitter. The deviation during operation of the division ratio from the 1:1 ratio significantly affects the statistical properties of the generated noise. In [13], a heater inserted into one of the arms of the Mach-Zehnder integrated-optical interferometer was used to solve the problem of controlling the division ratio. This provided a controlled phase shift for fine tuning the division ratio. In this case, a silicon chip was used as a substrate. The experimentally demonstrated bandwidth of quantum noise generation in this case was no more than 0.1 GHz.
Practical implementation of a quantum noise generator
We have proposed and implemented a quantum noise generator circuit free from the above disadvantages. A schematic of a broadband quantum noise generator with an electrically controlled beam splitter in an integrated-optical design is shown in Fig. 3. A semiconductor DFB laser with a wavelength of 1552 nm, a spectral width of 170 kHz, and a power of 100 mW was used as a local oscillator (1).
An electrically controlled beam splitter is a Mach-Zehnder integrated optical interferometer with one input and two outputs (2). The waveguides (3) were manufactured using the well-proven titanium-diffusion technology, which provides minimal optical losses in the waveguides [1, 2].
The laser (1) together with the integrated optical beam splitter (2) and the balanced photodetector form a physical source of entropy.
One of the differences between our generator is the use of electro-optical control of the splitting ratio. Such control was realized due to a pair of electrodes (4) applied along the waveguide of one of the interferometer arms. By changing the voltage applied to the electrodes, it was possible to control the division ratio in real time with an accuracy of at least 0.1%.
A pair of InP photodetectors A and B, connected as shown in Fig. 3, formed a balanced detector (5). The sensitivity of each photodetector was 0.78 A / W, and the dark current was less than 10 μA. The laser (1), the beam splitter (2), and the balanced detector (5) are interconnected by standard PM optical fibers.
An analog electrical signal from the output of the balanced detector (5) was investigated using a broadband spectrum analyzer. Fig. 3, on the right, shows the signal spectra at the output of the balanced detector. Curve (1) – local oscillator is off, curve (2) – local oscillator is on. Hence, it is possible to estimate the bandwidth of quantum noise generation at least 4 GHz.
Discussion of the results
As follows from the literature review presented here, the 4 GHz noise generation bandwidth that we have achieved using an entropy source based on quantum fluctuations is currently a record one.
For practical applications, both the quantum generation of broadband noise and the generation of truly random sequences are urgent problems. In this work, we have demonstrated a practical solution to only the first problem – the generation of broadband noise. Obviously, the second task, the generation of a truly random sequence, can be solved by using an analog-to-digital converter with the required parameters included at the output of the noise generator.
It is useful to estimate the potential performance of a quantum random number generator based on our noise source. The experimentally measured values of the operating frequency band (~4 GHz) and dynamic range (~12 dB) give an estimate of the potential maximum performance of the random number generator of the order of 4 · 109 · 4 = 16 · 109 [Hz] × [bit]. It is important to note that this performance has been demonstrated on a laboratory model; the parameters can still be significantly optimized.
ABOUT AUTHORS
Viktor Petrov, Doctor of Physical and Mathematical Sciences (Radiophysics), Doctor of Physical and Mathematical Sciences (Optics); e-mail: vmpetrov@itmo.ru; Chief Researcher, National Research University ITMO, St. Petersburg, Russia.
ORCID: 0000 0002 8523 0336
Shamrаy Alexander Valerievich, Doctor of Physical and Mathematical Sciences; e-mail: Achamrai@mail.ioffe.ru; Head. lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0003 0292 8673
Il’ichev Igor Vladimirovich, candidate of chemical sciences, senior researcher, lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0001 7803 0630
Agruzov Petr Mikhailovich, junior researcher, lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0002 1248 7069
Lebedev Vladimir Vladimirovich, junior researcher, lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0003 0292 8673
Contribution by the members
of the team of authors
The article was prepared on the basis of many years of work by all members of the team of authors.
Conflict of interest
The authors claim that they have no conflict of interest. All authors took part in writing the article and supplemented the manuscript in part of their work.
V. M. Petrov 1, A. V. Shamray 2, I. V. Ilyichev 2, P. M. Agruzov 2, V. V. Lebedev 2
ITMO National Research University, St. Petersburg, Russia
A. F. Ioffe PTI of RAS, St. Petersburg, Russia
The work of a quantum noise generator in a band of at least 4 GHz, and with an excess of quantum noise over classical ones by 12–13 dB was demonstrated for the first time. The novel main element of such generator, an optical beam splitter with an electrically controlled splitting ratio, is made in the form of an integrated optical Mach-Zehnder interferometer on a lithium niobate substrate.
Keywords: quantum communications, microwave integrated optical modulators, quantum noise generator
Received on: 12.01.2021
Accepted on: 04.02.2021
Introduction
Generating noise as well as generating sequences of random numbers is the backbone of the modern digital economy. Sequences of random numbers are used in security systems, cryptography, scientific research, generating QR codes, blockchains, as well as in games, i. e. in all those practical applications where the task of generating truly random numbers is paramount. In the Russian Federation, special attention is paid to ensuring information security, which follows from the doctrine of “Information security of the Russian Federation”, approved by Decree of the President of the Russian Federation No. 646 dated December 5, 2016.
Our recent successes [1–3] related to the creation of high-quality controllable integrated-optical devices allowed us to create a compact quantum noise generator based on an electrically controlled integrated-optical beam splitter, made according to the Mach-Zehnder interferometer scheme.
Development status
The idea of using a circuit of a quantum noise generator based on vacuum fluctuations (see Fig. 1), containing a local oscillator (laser), an optical beam splitter BS, two photodetectors A, B and a circuit for subtracting electrical signals A-B from photodetectors (balanced detector) is known [4, 5]. The principle of operation of such a device is based on one of the fundamental phenomena of quantum physics – vacuum fluctuations VF [6]. It is generally accepted that the Lamb shift [7] and the Casimir interaction [8, 9] are direct confirmation of the existence of vacuum fluctuations.
Practical implementations of this scheme are described in the literature. In [4], such a scheme was theoretically analyzed, and, based on the element base available at that time, estimates were given of the possible performance of a random number generator based on it – 200 Mbit / s. In [10], an analysis of a similar scheme gave a potential estimate of the performance of 70 Gb / s, and its experimental implementation on volumetric elements made it possible to achieve a noise generation bandwidth of 1.5–2.0 GHz. In [11], the experimentally demonstrated bandwidth of the quantum generation of white noise was approximately 1.9 GHz, in [12] – approximately 0.4…0.5 GHz.
One of the main requirements for the elements of such a device is a high accuracy and stability in time of the division ratio of the beam splitter. The deviation during operation of the division ratio from the 1:1 ratio significantly affects the statistical properties of the generated noise. In [13], a heater inserted into one of the arms of the Mach-Zehnder integrated-optical interferometer was used to solve the problem of controlling the division ratio. This provided a controlled phase shift for fine tuning the division ratio. In this case, a silicon chip was used as a substrate. The experimentally demonstrated bandwidth of quantum noise generation in this case was no more than 0.1 GHz.
Practical implementation of a quantum noise generator
We have proposed and implemented a quantum noise generator circuit free from the above disadvantages. A schematic of a broadband quantum noise generator with an electrically controlled beam splitter in an integrated-optical design is shown in Fig. 3. A semiconductor DFB laser with a wavelength of 1552 nm, a spectral width of 170 kHz, and a power of 100 mW was used as a local oscillator (1).
An electrically controlled beam splitter is a Mach-Zehnder integrated optical interferometer with one input and two outputs (2). The waveguides (3) were manufactured using the well-proven titanium-diffusion technology, which provides minimal optical losses in the waveguides [1, 2].
The laser (1) together with the integrated optical beam splitter (2) and the balanced photodetector form a physical source of entropy.
One of the differences between our generator is the use of electro-optical control of the splitting ratio. Such control was realized due to a pair of electrodes (4) applied along the waveguide of one of the interferometer arms. By changing the voltage applied to the electrodes, it was possible to control the division ratio in real time with an accuracy of at least 0.1%.
A pair of InP photodetectors A and B, connected as shown in Fig. 3, formed a balanced detector (5). The sensitivity of each photodetector was 0.78 A / W, and the dark current was less than 10 μA. The laser (1), the beam splitter (2), and the balanced detector (5) are interconnected by standard PM optical fibers.
An analog electrical signal from the output of the balanced detector (5) was investigated using a broadband spectrum analyzer. Fig. 3, on the right, shows the signal spectra at the output of the balanced detector. Curve (1) – local oscillator is off, curve (2) – local oscillator is on. Hence, it is possible to estimate the bandwidth of quantum noise generation at least 4 GHz.
Discussion of the results
As follows from the literature review presented here, the 4 GHz noise generation bandwidth that we have achieved using an entropy source based on quantum fluctuations is currently a record one.
For practical applications, both the quantum generation of broadband noise and the generation of truly random sequences are urgent problems. In this work, we have demonstrated a practical solution to only the first problem – the generation of broadband noise. Obviously, the second task, the generation of a truly random sequence, can be solved by using an analog-to-digital converter with the required parameters included at the output of the noise generator.
It is useful to estimate the potential performance of a quantum random number generator based on our noise source. The experimentally measured values of the operating frequency band (~4 GHz) and dynamic range (~12 dB) give an estimate of the potential maximum performance of the random number generator of the order of 4 · 109 · 4 = 16 · 109 [Hz] × [bit]. It is important to note that this performance has been demonstrated on a laboratory model; the parameters can still be significantly optimized.
ABOUT AUTHORS
Viktor Petrov, Doctor of Physical and Mathematical Sciences (Radiophysics), Doctor of Physical and Mathematical Sciences (Optics); e-mail: vmpetrov@itmo.ru; Chief Researcher, National Research University ITMO, St. Petersburg, Russia.
ORCID: 0000 0002 8523 0336
Shamrаy Alexander Valerievich, Doctor of Physical and Mathematical Sciences; e-mail: Achamrai@mail.ioffe.ru; Head. lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0003 0292 8673
Il’ichev Igor Vladimirovich, candidate of chemical sciences, senior researcher, lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0001 7803 0630
Agruzov Petr Mikhailovich, junior researcher, lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0002 1248 7069
Lebedev Vladimir Vladimirovich, junior researcher, lab. of Quantum Electronics Physicotechnical Institute named after A. F. Ioffe, St. Petersburg, Russia.
ORCID: 0000 0003 0292 8673
Contribution by the members
of the team of authors
The article was prepared on the basis of many years of work by all members of the team of authors.
Conflict of interest
The authors claim that they have no conflict of interest. All authors took part in writing the article and supplemented the manuscript in part of their work.
Readers feedback
