---
title: QkBitTerm (latest version)
description: API reference for QkBitTerm in the latest version of qiskit-c
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-c/qk-bit-term
---

# QkBitTerm

```c
enum QkBitTerm
```

An enum that to represent each of the single-qubit alphabet terms enumerated below.

## Values

- **`QkBitTerm_X`**

  The Pauli $X$ operator.

  Value: 2 (`0b0010`)

- **`QkBitTerm_Y`**

  The Pauli $Y$ operator.

  Value: 3 (`0b0011`)

- **`QkBitTerm_Z`**

  The Pauli $Z$ operator.

  Value: 1 (`0b0001`)

- **`QkBitTerm_Plus`**

  The projector $\lvert +\rangle\langle +\rvert$ to the positive $X$ eigenstate.

  Value: 10 (`0b1010`)

- **`QkBitTerm_Minus`**

  The projector $\lvert -\rangle\langle -\rvert$ to the negative $X$ eigenstate.

  Value: 6 (`0b0110`)

- **`QkBitTerm_Right`**

  The projector $\lvert r\rangle\langle r\rvert$ to the positive $Y$ eigenstate.

  Value: 11 (`0b1011`)

- **`QkBitTerm_Left`**

  The projector $\lvert l\rangle\langle l\rvert$ to the negative $Y$ eigenstate.

  Value: 7 (`0b0111`)

- **`QkBitTerm_Zero`**

  The projector $\lvert 0\rangle\langle 0\rvert$ to the positive $Z$ eigenstate.

  Value: 9 (`0b1001`)

- **`QkBitTerm_One`**

  The projector $\lvert 1\rangle\langle 1\rvert$ to the negative $Z$ eigenstate.

  Value: 5 (`0b0101`)

## Representation

The enum is stored as single byte, its elements are represented as unsigned 8-bit integer.

```c
typedef uint8_t QkBitTerm
```

> **Warning**
>
> Not all `uint8_t` values are valid bit terms. Passing invalid values is undefined behavior.

The numeric structure of these is that they are all four-bit values of which the low two bits are the (phase-less) symplectic representation of the Pauli operator related to the object, where the low bit denotes a contribution by $Z$ and the second lowest a contribution by $X$, while the upper two bits are `00` for a Pauli operator, `01` for the negative-eigenstate projector, and `10` for the positive-eigenstate projector.

## Functions

### qk\_bitterm\_label

`uint8_t qk_bitterm_label(QkBitTerm bit_term)`

Get the label for a bit term.

#### Example

```c
QkBitTerm bit_term = QkBitTerm_Y;
// cast the uint8_t to char
char label = qk_bitterm_label(bit_term);
```

#### Safety

The behavior is undefined if `bit_term` is not a valid `uint8_t` value of a `QkBitTerm`.

**Parameters**

- **bit\_term** – The bit term.

**Returns**

The label as `uint8_t`, which can be cast to `char` to obtain the character.