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Once Alice obtains her qubit in the entangled state, she applies a certain quantum gate to her qubit depending on which two-bit message (00, 01, 10 or 11) she wants to send to Bob. Her entangled qubit is then sent to Bob who, after applying the appropriate quantum gate and making a measurement , can retrieve the classical two-bit message.
The qubit held by Alice (subscript "A") can be in a superposition of 0 and 1. If Alice measured her qubit in the standard basis, the outcome would be either 0 or 1, each with probability 1/2; if Bob (subscript "B") also measured his qubit, the outcome would be the same as for Alice. Thus, Alice and Bob would each seemingly have random outcome.
The general definition of a qubit as the quantum state of a two-level quantum system.In quantum computing, a qubit (/ ˈ k juː b ɪ t /) or quantum bit is a basic unit of quantum information—the quantum version of the classic binary bit physically realized with a two-state device.
Unlike classical digital states (which are discrete), a qubit is continuous-valued, describable by a direction on the Bloch sphere. Despite being continuously valued in this way, a qubit is the smallest possible unit of quantum information, and despite the qubit state being continuous-valued, it is impossible to measure the value precisely ...
Errors and lost qubits will affect Bob's measurements, resulting in holes in Bob's measurement table. Significant losses in measurement will affect Bob's ability to verify Alice's qubit sequence in step 5. One theoretically surefire way for Alice to cheat is to utilize the Einstein-Podolsky-Rosen (EPR) paradox.
Now suppose Alice is an observer for system A, and Bob is an observer for system B. If in the entangled state given above Alice makes a measurement in the { | 0 , | 1 } {\displaystyle \{|0\rangle ,|1\rangle \}} eigenbasis of A , there are two possible outcomes, occurring with equal probability: Alice can obtain the outcome 0, or she can obtain ...
In matters relating to quantum information theory, it is convenient to work with the simplest possible unit of information: the two-state system of the qubit.The qubit functions as the quantum analog of the classic computational part, the bit, as it can have a measurement value of both a 0 and a 1, whereas the classical bit can only be measured as a 0 or a 1.
Alice then announces those two states. Alice will note whether the state is the computational basis state or the Hadamard basis state; that piece of information makes up the secret bit that Alice wishes to communicate to Bob. Bob now knows that the state of his qubit was one of the two states indicated by Alice. To determine the secret bit, Bob ...