2.1. Application Scenario
The Internet of Things (IoT) is a framework that uses internet technology to connect various smart devices and achieve information sharing and interaction. The IoT is widely used in many fields, such as smart homes, intelligent transportation, smart medical care, etc. However, the IoT also faces security issues, such as device identity authentication, data confidentiality and integrity, network defence, etc. To cope with these challenges, the quantum secret communication protocol provides a new solution. The quantum secret communication protocol is a technology that uses quantum mechanics principles, such as quantum superposition, quantum entanglement, quantum no-cloning, etc., to achieve information-secure transmission and encryption. It can effectively resist eavesdropping and interference from third parties and ensure the security and reliability of IoT communication. This paper will discuss a scenario that uses a quantum secret communication protocol to protect IoT communication security.
Device A and device B are edge devices in the IoT that are close to the data source or the user and can process and analyze data locally. Device A is equipped with multiple sensors, which can collect environmental data, such as temperature, pressure, etc. Device B can receive the environmental status of other edge devices and issue corresponding instructions according to the status change. Control node C and control node D are cloud computing devices that are responsible for the authentication and control services of the IoT and ensure the security of the IoT. These devices transmit classical data through classical network channels and exchange quantum information through quantum channels, as shown in
Figure 1.
Device A must securely transmit the environmental state data (such as temperature, pressure, etc.) to another device, device B, within the IoT system. This transmission of the environmental state exists at a general level of security within the entire IoT system; thus necessitating authorization solely from control node C. Device A can encode the intended state information into a quantum state, denoted as state a, and employ controlled quantum teleportation to transmit this quantum state to device B. By measuring the received quantum state a, device B can retrieve the environmental state information from device A’s side. Conversely, device B controls device A, allowing it to make determinations based on the transmitted environmental state data and issue control commands to device A. Considering the security of the IoT system, this manipulation operates at a higher level of protection throughout the entire IoT system, requiring joint authorization from control nodes C and D. Device B can encode the desired instructions into a quantum state, denoted as state b, and utilizing remote quantum state preparation under the shared control of control nodes C and D, create a quantum state on device A’s side that matches the state of quantum state b. Device A can measure the quantum state to decode the instruction.
Based on the scenario of using a quantum secret communication protocol to ensure the security of IoT communication, this paper proposes an HCHQC protocol that uses a six-qubit entangled state as the quantum channel and realizes the layered control of two different communication protocols, quantum invisible transmission, and remote quantum state preparation, on one quantum channel. In the communication scheme, device A and device B represent Alice and Bob, respectively, and control node C and control node D represent Charlie and David, respectively. The following
Section 2, will detail this hybrid quantum communication scheme that uses a six-qubit entangled state as the quantum channel for the IoT.
2.2. Specific Communication Plan
The communication scheme introduced in this section has the following advantages: (1) flexible communication, which can be controlled according to the task requirements and security levels; (2) quantum resource saving, which can complete two tasks with one six-qubit entangled state; (3) high communication efficiency, which can transmit and reconstruct states with a small amount of classical information and quantum operations. Next, we will explain this scheme in detail.
Assume Alice has an arbitrary unknown single-qubit state, denoted as:
where
and
are complex numbers satisfying
.
Alice wants to teleport an unknown single qubit state
to Bob using quantum teleportation. Meanwhile, Bob wants to prepare a known single qubit state
on Alice’s side through remote state preparation. The state of
can be written as:
where
and
are real numbers satisfying
.
At this point, assuming that the quantum channel shared by Alice, Bob, Charlie, and David is a six-qubit entangled quantum state, it can be expressed as:
Among them, qubits
and
belong to Alice, qubits
and
belong to Bob, qubit
C belongs to Charlie, and qubit
D belongs to David. The quantum state of the whole system can be expressed as follows:
where ⊗ represents the tensor product. We now introduce the hybrid quantum communication scheme in four steps.
Alice performs a joint measurement on two qubits
a and
she possesses, using the Bell measurement basis given by the following expression:
Alice can obtain one of the four possible measurement results with equal probability, and the remaining qubits
,
,
,
C, and
D will collapse into one of the corresponding four states
,
,
, or
, as shown in
Table 1.
At the same time, Bob performs projection measurement on his qubit
, and the measurement basis is:
Since the coefficients
and
are known to Bob, such a set of measurement bases can be obtained. The projection measurements and the states of the remaining qubits are shown in
Table 2 below.
Alice needs Charlie’s help to complete the task of quantum teleporting the quantum state
to Bob using quantum entanglement. Suppose Charlie agrees to assist Alice and Bob. In that case, he needs to perform a von Neumann measurement on his qubit
C on the basis
and communicate the measurement result to Bob through the classical communication channel. The measurement basis
is as follows:
Now suppose a situation exists where, before Charlie performs a single-qubit von Neumann measurement, the measurement results of Alice and Bob are
and
, respectively, then the remaining qubits will collapse to the state
. After Charlie performs the von Neumann measurement on qubit C, if the obtained measurement result is
, the state of the remaining qubits will collapse to:
We can go one step further and write the equation as follows:
It can be clearly seen that after Bob learns the measurement result of Charlie through the classical channel, he only needs to perform the
gate operation on the qubit
to correct the quantum state. Then he can obtain the quantum state
. However, the qubits
and
D are still entangled, so Alice cannot obtain the state
prepared remotely by Bob. The other cases and the unitary operations corresponding to each case are shown in
Table 3.
To remotely prepare the quantum state from Bob to Alice, supervisors Charlie and David are needed. David must perform the qubit D single-qubit von Neumann measurements. Once Alice receives the measurement results from Charlie and David through the classical channel, she can perform the corresponding unitary operation on qubit to obtain the desired quantum state that Bob intends to prepare.
In Step 3’s example, if David’s measurement result is
, then Alice will obtain the collapsed state of qubit
as
. To reconstruct the quantum state
, Alice can perform the unitary operation
I on
. On the other hand, if David’s measurement result is
, then Alice will observe the collapsed state of qubit
as
. To reconstruct the quantum state
, Alice can perform the unitary operation
on
. The details of David’s measurement results, the state of qubit
, and Alice’s unitary operation are presented in
Table 4.
The four unitary operations used in the transmission process are:
The above steps illustrate how a hybrid quantum communication system is implemented using a six-qubit entangled state as a channel. During the transmission process, Alice sends the state of qubit a to Bob via quantum teleportation, which Charlie supervises. Simultaneously, Bob prepares a qubit in the same state as qubit b on Alice’s side through remote state preparation, which Charlie and David jointly supervise. This approach allows different communication protocols to be controlled on a quantum channel, improving communication flexibility.