Supported Gates¶

Clifft parses Stim circuit format and supports nearly all Stim gates, plus non-Clifford extensions.

Pauli Gates¶

Gate	Notes
`X`	Pauli X
`Y`	Pauli Y
`Z`	Pauli Z

All Pauli gates are single-qubit Cliffords absorbed at compile time (zero VM cost).

Single-Qubit Clifford Gates¶

Gate	Notes
`H`	Hadamard (alias: `H_XZ`)
`S`	Phase gate (alias: `SQRT_Z`)
`S_DAG`	Inverse phase gate (alias: `SQRT_Z_DAG`)
`SQRT_X`, `SQRT_X_DAG`	Square root of X and inverse
`SQRT_Y`, `SQRT_Y_DAG`	Square root of Y and inverse
`H_XY`, `H_NXY`	Hadamard variants in X,Y plane
`H_YZ`, `H_NYZ`	Hadamard variants in Y,Z plane
`H_NXZ`	Negated Hadamard
`C_XYZ`, `C_ZYX`, `C_NXYZ`, `C_NZYX`, `C_XNYZ`, `C_XYNZ`, `C_ZNYX`, `C_ZYNX`	Period-3 Clifford rotations

All single-qubit Cliffords are absorbed AOT — they update the Clifford frame \(U_C\) at compile time and have zero cost at runtime.

Non-Clifford Extensions¶

Clifft extends Stim with discrete and arbitrary-angle non-Clifford gates. These operations can activate qubits in the virtual machine and expand the active state vector.

T Gates¶

Gate	Notes
`T`	\(\pi/8\) gate
`T_DAG`	Inverse \(\pi/8\) gate

Continuous Rotations¶

Clifft extends the Stim gate set with arbitrary-angle rotation gates. All angle parameters are in half-turns (multiply by pi to get radians).

Single-Qubit Rotations¶

Gate	Syntax	Notes
`R_X`	`R_X(alpha) target`	Rotation about X axis by `alpha * pi` radians
`R_Y`	`R_Y(alpha) target`	Rotation about Y axis by `alpha * pi` radians
`R_Z`	`R_Z(alpha) target`	Rotation about Z axis by `alpha * pi` radians
`U3`	`U3(theta,phi,lambda) target`	General SU(2) gate = `R_Z(phi) R_Y(theta) R_Z(lambda)`
`U`	`U(theta,phi,lambda) target`	Alias for `U3`

Name conflicts with Stim

Clifft uses R_X, R_Y, R_Z (with underscores) to avoid collision with Stim's RX / RY reset-in-basis instructions.

Two-Qubit Pauli Rotations¶

Gate	Syntax	Notes
`R_XX`	`R_XX(alpha) q0 q1`	`exp(-i * alpha * pi/2 * XX)`
`R_YY`	`R_YY(alpha) q0 q1`	`exp(-i * alpha * pi/2 * YY)`
`R_ZZ`	`R_ZZ(alpha) q0 q1`	`exp(-i * alpha * pi/2 * ZZ)`

Duplicate target qubits (e.g. R_XX(0.5) 3 3) are rejected at parse time.

Multi-Qubit Pauli Rotation¶

Gate	Syntax	Notes
`R_PAULI`	`R_PAULI(alpha) X0Y1Z2`	Arbitrary Pauli product rotation

The target list uses Stim's Pauli product syntax (e.g. X0*Y1*Z2). Maximum target count is 64 qubits per instruction.

Two-Qubit Clifford Gates¶

Gate	Notes
`CX` / `CNOT` / `ZCX`	Controlled-X
`CY` / `ZCY`	Controlled-Y
`CZ` / `ZCZ`	Controlled-Z
`SWAP`	Qubit swap
`ISWAP`, `ISWAP_DAG`	Imaginary swap and inverse
`CXSWAP`, `SWAPCX`	CX+SWAP composites
`CZSWAP`	CZ+SWAP composite (alias: `SWAPCZ`)
`SQRT_XX`, `SQRT_XX_DAG`	Square root of XX and inverse
`SQRT_YY`, `SQRT_YY_DAG`	Square root of YY and inverse
`SQRT_ZZ`, `SQRT_ZZ_DAG`	Square root of ZZ and inverse
`XCX`, `XCY`, `XCZ`	X-controlled gates
`YCX`, `YCY`, `YCZ`	Y-controlled gates

Two-qubit Cliffords are also absorbed at compile time.

Measurements and Resets¶

Instruction	Notes
`M` / `MZ`	Z-basis measurement
`MX`	X-basis measurement
`MY`	Y-basis measurement
`MR` / `MRZ`	Measure + reset (Z-basis)
`MRX`	Measure + reset (X-basis)
`MRY`	Measure + reset (Y-basis)
`R` / `RZ`	Reset to \(\\|0\rangle\)
`RX`	Reset to \(\\|+\rangle\)
`RY`	Reset to \(\\|{+i}\rangle\)

Multi-Qubit Measurements¶

Instruction	Notes
`MPP`	Multi-Pauli product measurement
`MXX`	Pair XX measurement (desugared to MPP)
`MYY`	Pair YY measurement (desugared to MPP)
`MZZ`	Pair ZZ measurement (desugared to MPP)

Noise Channels¶

Instruction	Notes
`DEPOLARIZE1(p)`	Single-qubit depolarizing noise
`DEPOLARIZE2(p)`	Two-qubit depolarizing noise
`X_ERROR(p)`	Single-qubit X error
`Y_ERROR(p)`	Single-qubit Y error
`Z_ERROR(p)`	Single-qubit Z error
`PAULI_CHANNEL_1(px,py,pz)`	General single-qubit Pauli channel
`PAULI_CHANNEL_2(...)`	General two-qubit Pauli channel (15 params)

Noisy measurements (e.g., M(0.01) 0) are decomposed by the parser into a clean measurement followed by an internal READOUT_NOISE instruction that models classical bit-flip errors on the measurement result.

Identity Gates¶

Gate	Notes
`I`	Single-qubit identity (parsed but not emitted)
`II`	Two-qubit identity (parsed but not emitted)
`I_ERROR`	Single-qubit identity error (no-op)
`II_ERROR`	Two-qubit identity error (no-op)

These are accepted for compatibility with Stim circuits but have no effect.

Annotations and Control Flow¶

Instruction	Notes
`REPEAT N { ... }`	Loop (unrolled at parse time)
`DETECTOR`	QEC detector declaration
`OBSERVABLE_INCLUDE`	Observable accumulator
`MPAD`	Deterministic measurement padding
`TICK`	Timing layer marker
`QUBIT_COORDS`	Coordinate annotation (discarded)
`SHIFT_COORDS`	Coordinate shift (discarded)

Expectation Value Probes¶

Instruction	Syntax	Notes
`EXP_VAL`	`EXP_VAL X0Y1Z2`	Non-destructive expectation value probe

EXP_VAL evaluates the expectation value of one or more Pauli products at the exact point in the circuit where it appears. It uses the same Pauli product syntax as MPP — multiple whitespace-separated products per instruction are supported, each producing one float64 result in [-1, 1].

H 0
EXP_VAL X0          # single Pauli: <X> on qubit 0
EXP_VAL X0*Y1*Z2    # multi-qubit product
EXP_VAL X0*X1 Z0*Z1 # two products in one instruction

Results are available via SampleResult.exp_vals (shape (shots, num_exp_vals)).

Not Yet Supported¶

Gate	Category	Reason
`CORRELATED_ERROR` / `E`	Noise	Correlated multi-qubit error model
`ELSE_CORRELATED_ERROR`	Noise	Depends on `CORRELATED_ERROR`
`HERALDED_ERASE`	Noise	Heralded erasure not modeled
`HERALDED_PAULI_CHANNEL_1`	Noise	Heralded channel not modeled
`SPP`, `SPP_DAG`	Pauli product	Stochastic Pauli product gate