English translation of the original Chinese article. Publication dates and the extent of recovered text are preserved. Figures retain their original labels. Read the Chinese original.
Delft University of Technology, Netherlands / Precision Microsystem & Engineering
PhD: Tsinghua University / Mechanical Engineering
Keywords: quantum computers, qubits, measurement, entanglement, human society
You may often see the term “quantum computer” in the news. Once anything becomes associated with “quantum,” you probably find it baffling and immediately lose interest. This article will take you into the fascinating world of quantum computers.
Classical digital computers normally encode information using 0 and 1. Their most basic unit is the bit, which is either 0 or 1. The basic unit of a quantum computer is the quantum bit, or qubit. A qubit can be in a superposition such as α|0⟩ + β|1⟩, where |α|² + |β|² = 1. When measured in the 0, 1 basis, the probabilities of obtaining 0 and 1 are |α|² and |β|², respectively; they need not each be 50%. Superposition does not mean that “it was already some classical 0 or 1, but we simply did not know which.” The life stories below are only metaphors to aid understanding. Everyday choices and social relationships must not be treated as actual quantum measurements or entanglement.
The birth of a qubit is like that of a newborn baby: neither has a predictable path through life. Everyone was probably asked in childhood what they wanted to be when they grew up, because life then seemed full of possibilities. Mr. Qubit’s life is rather more unfortunate, though: he has only two options—to grow up to be 1 or to be 0. This choice is called “measurement.” Before “measurement,” a qubit may yield 1 or 0. We know that all instructions in ordinary computers consist of 0s and 1s. In a quantum computer, reading out a calculation usually requires measurements at the appropriate steps, yielding classical 0s or 1s. If a measurement yields 1, the unobserved outcome 0 cannot also be read out in that same measurement. Experiments can, however, repeatedly prepare the same quantum state to determine the probabilities of different outcomes. This still differs from the metaphor of living only once. It is like choosing a university after the college entrance examination: you could choose Tsinghua, viewed as state 1, or Peking University, viewed as state 0, and you must decide within a specified period. Once the choice is made, you will never know what life studying at the other university would have been like—perhaps that is why such questions are so popular on Douban. Of course, the beauty of life is that you have many opportunities to choose, or “measure,” and alter your course. Even so, you must ultimately take responsibility for each choice, because, like a qubit, you can experience only one life.
Once you understand these features of qubits, you will naturally ask what advantages they offer over bits. The state of n qubits can involve amplitudes for 2ⁿ computational basis states, but that does not mean that 2ⁿ independent classical data items can be put into them and then read out one by one. Measuring n qubits in the computational basis produces one n-bit string at a time. Nor can two independent classical bits be directly read out from one qubit. The potential of quantum algorithms comes from controlling resources such as superposition, interference, and entanglement, rather than treating measurement as a free way of reading an exponential amount of data.
As mentioned above, the probabilities of measuring a qubit as 0 or 1 can differ. These are determined by the amplitudes of its quantum state, not necessarily by entanglement with other qubits. Classical bits can also be correlated. Quantum entanglement is a nonclassical correlation that cannot be described as a simple combination of independent states of the constituent parts; multiple qubits may or may not be entangled. This is somewhat like human society: everyone is a social being, and each decision is inevitably influenced to some degree by other people. In that figurative sense, people too have “entanglements”—the loves, hatreds, attachments, and strangers we often talk about. Returning to the subject, people use multiple qubits to store information and perform computations. When needed, some qubits are “measured” together. For each individual qubit, whether this measurement produces 0 or 1 is not determined by it alone; it also depends on the other qubits. The extent of entanglement cannot be judged solely from spatial distance; noise, loss, and decoherence in real systems affect its preservation. One measurement yields one outcome of the qubit combination, and cannot simultaneously read out the other outcomes that did not occur. Repeated preparation and measurement can nevertheless reveal their statistical distribution. This is like having many romantic relationships but ultimately marrying only one person—making a measurement. Marriage, of course, is not a one-person affair; it is an “entanglement” between two people. In China, that means an “entanglement” of at least six people in two families. According to the theory that knowing six people connects you with everyone in the world, one marriage means you are influencing the whole world. Likewise, your mutual influence with nearby people is naturally greater, while your influence with distant people is weaker. Perhaps one afternoon many years later you will imagine what life would have been like had you married someone else, and how that would have affected the world. Of course, none of this can be known. From this perspective, does human society resemble an enormous, complex, yet exquisitely precise “super quantum computer”?
Next, a brief explanation of how qubits are produced. There are many ways to implement a qubit. One uses a superconducting circuit containing a Josephson junction. A transmon, for example, encodes 0 and 1 using two low-energy quantum states of the circuit, with control pulses preparing and manipulating superpositions. It does not automatically generate a superposition through the random appearance of clockwise or counterclockwise currents. Producing more stable and controllable qubits remains an important problem. As a research example from the era of the original article, teams at Google and the University of California, Santa Barbara reported a device consisting of nine superconducting qubits in 2015. Repeated parity checks demonstrated error detection and state protection; this did not mean that a general-purpose quantum computer capable of handling arbitrary large problems had already been built.
Finally, this article closes with a passage from Milan Kundera’s The Unbearable Lightness of Being, to reflect on the wonder of a quantum life:
“There is no way to test which choice is good, because there is no comparison. Everything is experienced immediately, only once, without preparation. It is as though an actor goes onstage without rehearsal. If life’s first rehearsal is already life itself, what value can life have? For this reason, life is always like a sketch, though ‘sketch’ is not quite the right word: a sketch is the preliminary form of something, such as the draft of a picture. But the sketch of our life is not a draft of anything. It is a sketch that can never become a finished picture.”
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Revision Note: October 10, 2026
Revision dated 2026-10-10: Corrected the descriptions of quantum superposition and measurement; the misrepresentation of a 2ⁿ-dimensional state space as 2ⁿ classical data items that can be read out directly; the identification of ordinary correlation with entanglement; and the claim that entanglement necessarily weakens with distance. Clarified the preparation of superconducting qubits and the 2015 nine-qubit experiment. The life analogies are retained as metaphors; the byline was recovered from the matching article retained in the WeChat account, and the historical date follows the old website record.
Additional References
- IBM Quantum Learning: Bits, gates, and circuits(Superposition, Born-rule measurement probabilities, multiple qubits, and measurement outputs)
- IBM Quantum Learning: Entanglement in action(The definition of quantum entanglement as nonclassical correlation)
- Hensen et al. (2015), Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres(Experiments with spatially separated entanglement; entanglement must not be equated with everyday influence between nearby people)
- Koch et al. (2007), Charge insensitive qubit design derived from the Cooper pair box(Transmon design with Josephson junctions and controlled quantum energy levels)
- Kelly et al. (2015), State preservation by repetitive error detection in a superconducting quantum circuit(The historical facts of the 2015 repeated error-correction experiment with nine superconducting qubits)
The text was recovered from the matching article retained in the WeChat account, with the original website’s publication record retained. The old WeChat promotional layout has been removed. Available original illustrations have been restored.
Editorial revision note: Revision dated 2026-10-10: Corrected the descriptions of quantum superposition and measurement; the misrepresentation of a 2ⁿ-dimensional state space as 2ⁿ classical data items that can be read out directly; the identification of ordinary correlation with entanglement; and the claim that entanglement necessarily weakens with distance. Clarified the preparation of superconducting qubits and the 2015 nine-qubit experiment. The life analogies are retained as metaphors; the byline was recovered from the matching article retained in the WeChat account, and the historical date follows the old website record.
