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International Journal of Theoretical Physics

One-bit photon polarization in two-photon experiments. An information mechanics perspective

Frederick W. Kantor

Published Mar 1, 1991• 1 citation
Publisher
DOI
10.1007/bf00674971

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Quantum key distribution is one of the essential developments to reduce the vulnerability in the security of the systems due to the emergence of quantum computers. As long as large-scale quantum computers emerge, all the systems will be vulnerable to attack. To secure the communication, we can use quantum key distribution protocols in the near future. In this work, I have experimentally verified the BB84 protocol with an eavesdropper. We have used a classical channel to send polarization states of light. Our source is a readily available He-Ne laser (632.8nm). To send secret Information in a secure way, we use Quantum key distribution. Sender Alice sends randomly chosen polarization states of light to Bob. The states Alice sends are |H>,|V>,|D>, and |A>, and similarly, Bob also selects some random basis and detects this Information. In this experiment, |H>,|V> states belong to the '+' basis and |D>,|A> on the 'X' basis. Detecting |H>,|D> states at the detector is considered as '1' and detecting |V>,|A> represents the '0' bit as the output. Alice and Bob can choose the basis randomly. We got these | H>,|V>,|D>, and |A> states by rotating the half-wave plate at angles respectively 0°,90°,45°, and -45°. We used a motorized rotator to rotate the two half-wave plates, one at Alice's side and one at Bob's side, to select the basis and generate these states. The motorized rotator runs on a python code. Python code is designed in such a way that it can generate random bits and can run Alice and Bob parts simultaneously. A polarized beam splitter is used just before the detector to split the beam into | H> and |V> states with 100% intensity at one detector and 0% at the other and |D> and |A> states with 50:50 intensity. Therefore we used one half-wave plate just before the PBS, which can convert |H> and |V> states into |D> and |A> states when we rotate at these particular angles. Using this, we can detect |D> and |A> states with 100% intensity at one detector and 0% at the other. Based upon the basic choices of Alice and Bob, at the receiver part, Bob will receive the bits. At the end of the process, both parties will verify the basis. When the basis is matching, they will keep those bits, and which are not matching, they will discard them. The successful bits will become the encryption key. I did this experiment by sending 1000 bits, and 452 bits among them were successful. For the security analysis of this protocol, we implemented a third-person Eve who tries to steal the Information Alice sends to Bob. Eve used one Beam splitter to take half part of the light intensity and sent another half to Bob. Eve's part has one 50:50 beam splitter, which splits the beam into two. Then, one beam goes to a PBS, then to the detectors, and the other beam goes to a setup that has HWP and PBS, then to the detectors. In this experiment, Eve is successful in stealing the Information correctly. As we are using classical light, which has a huge number of photons, anyone can take some photons and execute a photon number splitting attack; the security of this process is very low. We need a single-photon source and a single photon detector to get total security from this protocol. Right now, I have done this experiment with the available pieces of equipment I have. When the needed types of equipment are available to me, I can implement the single-photon QKD experiment also. After the experiment, we realized that the superposition of states always holds in this experiment, but states do not collapse, as we are not performing the quantum measurement. Also, I have implemented the QKD protocol in the IBM Quantum lab, where Alice sends 1000 bits to Bob, and 474 bits among them were successful. Also, Eve’s interception was detected successfully.

•Jan 1, 2026•0 citations
This thesis presents the results of a series of four photonic experiments on the topic of quantum measurement. The first two experiments relate to quantum metrology, and the use of quantum states to increase the precision of measurements beyond what is possible with classical systems; first to detect and characterize decoherence, and then in the context of quantum imaging. The third experiment studies a fundamental question in quantum mechanics: "How much must a quantum system be disturbed by a measurement?". We use weak measurement to confirm a recent theoretical result, showing that if a particle's state is already sufficiently uncertain we can perform a measurement with very little disturbance -- contrary to common explanations of Heisenberg's uncertainty principle. The fourth experiment falls in the category of quantum computation. In quantum mechanics having multiple copies of an identical system allows us to extract more information than we can extract from a single copy (since quantum mechanics allows each system to be measured only once before collapsing). We present and experimentally implement a quantum algorithm to compress all of the "extractable information" present in an ensemble of identical copies of quantum bits into exponentially fewer quantum bits. The research presented here samples from a variety of topics in quantum information, showing in several contexts how fascinating quantum effects can be exploited to gain a "quantum enhancement".To enable these experiments two sources of entangled photons were built, and "hybrid" quantum systems (encoding information in multiple degrees of freedom of a photon) were used to implement quantum circuits. This thesis will present the details of one of these sources (a novel and practical source of entangled N00N states), which was used in a four-photon quantum metrology experiment. The other, more standard, source of polarization-entangled photon pairs will only briefly be reviewed to leave room for the discussion of hybrid quantum logic.
A method of creating all-optical devices for logic information processing is presented. The mechanism is based on virtual photon interaction in quantum field description, or dipole moment interaction in classical description. The device consists of two optical information bits channels and one optical bits channel of logic commands like AND, NOT, OR. A variety of logic operations can be achieved on one optical setup by polarization change of the logic bits which determines the logic commands. I present another application for the method as an information channels selector.
Quantum key distribution is one of the essential developments to reduce the vulnerability in the security of the systems due to the emergence of quantum computers. As long as large-scale quantum computers emerge, all the systems will be vulnerable to attack. To secure the communication, we can use quantum key distribution protocols in the near future. In this work, I have experimentally verified the BB84 protocol with an eavesdropper. We have used a classical channel to send polarization states of light. Our source is a readily available He-Ne laser (632.8nm). To send secret Information in a secure way, we use Quantum key distribution. Sender Alice sends randomly chosen polarization states of light to Bob. The states Alice sends are |H>,|V>,|D>, and |A>, and similarly, Bob also selects some random basis and detects this Information. In this experiment, |H>,|V> states belong to the '+' basis and |D>,|A> on the 'X' basis. Detecting |H>,|D> states at the detector is considered as '1' and detecting |V>,|A> represents the '0' bit as the output. Alice and Bob can choose the basis randomly. We got these | H>,|V>,|D>, and |A> states by rotating the half-wave plate at angles respectively 0°,90°,45°, and -45°. We used a motorized rotator to rotate the two half-wave plates, one at Alice's side and one at Bob's side, to select the basis and generate these states. The motorized rotator runs on a python code. Python code is designed in such a way that it can generate random bits and can run Alice and Bob parts simultaneously. A polarized beam splitter is used just before the detector to split the beam into | H> and |V> states with 100% intensity at one detector and 0% at the other and |D> and |A> states with 50:50 intensity. Therefore we used one half-wave plate just before the PBS, which can convert |H> and |V> states into |D> and |A> states when we rotate at these particular angles. Using this, we can detect |D> and |A> states with 100% intensity at one detector and 0% at the other. Based upon the basic choices of Alice and Bob, at the receiver part, Bob will receive the bits. At the end of the process, both parties will verify the basis. When the basis is matching, they will keep those bits, and which are not matching, they will discard them. The successful bits will become the encryption key. I did this experiment by sending 1000 bits, and 452 bits among them were successful. For the security analysis of this protocol, we implemented a third-person Eve who tries to steal the Information Alice sends to Bob. Eve used one Beam splitter to take half part of the light intensity and sent another half to Bob. Eve's part has one 50:50 beam splitter, which splits the beam into two. Then, one beam goes to a PBS, then to the detectors, and the other beam goes to a setup that has HWP and PBS, then to the detectors. In this experiment, Eve is successful in stealing the Information correctly. As we are using classical light, which has a huge number of photons, anyone can take some photons and execute a photon number splitting attack; the security of this process is very low. We need a single-photon source and a single photon detector to get total security from this protocol. Right now, I have done this experiment with the available pieces of equipment I have. When the needed types of equipment are available to me, I can implement the single-photon QKD experiment also. After the experiment, we realized that the superposition of states always holds in this experiment, but states do not collapse, as we are not performing the quantum measurement. Also, I have implemented the QKD protocol in the IBM Quantum lab, where Alice sends 1000 bits to Bob, and 474 bits among them were successful. Also, Eve’s interception was detected successfully.